image
Home Journals Progress in Chemistry
Progress in Chemistry

Abbreviation (ISO4): Prog Chem      Editor in chief: Jincai ZHAO

About  /  Aim & scope  /  Editorial board  /  Indexed  /  Contact  / 
Online first  /  Current issue  /  All issues  /  Top access  /  RSS

Progress in Chemistry >

2024 , Vol. 36 >Issue 10: 1490 - 1519

DOI: https://doi.org/10.7536/PC240206

综述

Organic Multifunctional Luminescent Materials Based on Modified Phenyl Derivatives

  • Yan Bing 1 ,
  • Xusen Yao 1 ,
  • Bing Mao 1 ,
  • Xiangyang Zhuang 1 ,
  • Hongji Jiang , 1, 2, 3, *
Expand
  • 1 State Key Laboratory of Organic Electronics and Information Displays (Nanjing University of Posts and Telecommunications), Nanjing 210023, China
  • 2 State Key Laboratory of Molecular Engineering of Polymers (Fudan University), Shanghai 200438, China
  • 3 State Key Laboratory of Luminescent Materials and Devices (South China University of Technology), Guangzhou 510641, China
*E-mail:

Received date: 2024-02-19

  Revised date: 2024-06-05

  Online published: 2024-07-01

Supported by

National Natural Science Foundation of China(21574068)

Major Research Program from the State Ministry of Science and Technology(2012CB933301)

Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)(YX030003)

State Key Laboratory Program of State Key Laboratory of Molecular Engineering of Polymers (Fudan University-k2023-21)

State Key Laboratory ofLuminescent Materials and Devices (South China University of Technology-2023-skllmd-21)

Fold

Abstract

The photoelectric properties of organic luminescent materials with large conjugated structures are closely related to molecular structure and intermolecular interaction. As a basic rigid conjugated unit between large π conjugation and C=X, phenyl has the characteristics of high stability, simple structure and direct relationship between structure and properties, and is the best model compound for studying the excited state properties of obtained luminescent materials. However, phenyl is a liquid at room temperature and becomes a solid at generally harsh low temperatures. Therefore, if the phenyl is fixed in a variety of environmentally responsive skeletons containing heteroatoms, and its condensed state structure and excited state properties will be effectively studied in a wide range, it will solve the important scientific problem of how the phenyl emollients can emit light under different aggregation states. In this paper, the recent advances in the modification of phenyl by heterocycles, conjugation extension of phenyl, substitution of peripheral heteroatoms, bridge between phenyl and other combined strategies are reviewed. The applications of modified phenyl in the synthesis of fluorescent materials, metal-organic complexes or clusters phosphorescent materials, thermally-activated delayed fluorescent materials, aggregation-induced luminescent materials and pure organic room temperature phosphorescent materials were reviewed according to different luminescence mechanisms. Finally, the future research focus and development prospect of organic multifunctional luminescent materials based on modified phenyl are also prospected.

Contents

1 Introduction

2 Fluorescent material based on phenyl derivatives

3 Metal-organic complexes or clusters phosphorescent materials based on phenyl derivatives

4 Thermally activated delayed fluorescence materials based on phenyl derivatives

5 Aggregation-induced emission materials based on phenyl derivatives

6 Pure organic room temperature phosphorescent materials based on phenyl derivatives

7 Organic multifunctional luminescent materials based on phenyl derivatives

Key words： phenyl; chemically modified; organic multifunctional luminescent materials; fluorescence; metal-organic complexes or clusters phosphorescence; thermally activated delayed fluorescence; aggregation-induced emission; pure organic room temperature phosphorescence

Cite this article

Yan Bing , Xusen Yao , Bing Mao , Xiangyang Zhuang , Hongji Jiang . Organic Multifunctional Luminescent Materials Based on Modified Phenyl Derivatives[J]. Progress in Chemistry, 2024 , 36(10) : 1490 -1519 . DOI: 10.7536/PC240206

1 Introduction

The emission color, intensity, and lifetime of organic luminescent materials can be modulated by altering molecular structure and aggregation states, with broad application prospects in anti-counterfeiting, sensors, data recording and storage, and organic light-emitting diodes (OLEDs). According to different luminescence mechanisms, organic luminescent materials can be categorized into fluorescent materials[1], phosphorescent materials[2], and delayed fluorescence[3]. Upon excitation, the excited excitons transition from the ground state S0 to a singlet state Sn, then through vibrational relaxation reach the lowest excited singlet state (S1), and finally emit fluorescence as they return from S1 to S0. Fluorescence, which only utilizes Sn excitons for emission, has low efficiency, with an internal quantum efficiency (IQE) capped at 25%, limiting its application potential. When the excitons on S1 undergo intersystem crossing (ISC) to the lowest excited triplet state (T1), the subsequent radiative transition from T1 to S0 produces phosphorescence. The triplet Tn excitons of organic molecules[4] are susceptible to oxygen and heat, leading to non-radiative relaxation and triplet annihilation, hence phosphorescence is mostly observed at low temperatures. Metal-organic complex phosphorescent materials, which promote ISC via spin-orbit coupling (SOC)[5,6], can utilize both Sn and Tn excitons, theoretically achieving an IQE of 100% and enabling room temperature phosphorescence (RTP). However, the heavy metals introduced are expensive and environmentally harmful. Therefore, pure organic RTP materials, due to their environmental friendliness, simple processing, good biodegradability, and low cost, have been extensively studied[7,8]. Nevertheless, organic RTP materials often suffer from inefficient ISC that cannot compete with ultrafast non-radiative transitions, making the design of efficient small-molecule organic RTP materials a challenge. When the excitons in the T1 state undergo reverse intersystem crossing (RISC) back to the S1 state and then radiatively decay to S0, delayed fluorescence is produced. In thermally activated delayed fluorescence (TADF) materials, the thermally activated T1 excitons undergo RISC to the S1 state, effectively utilizing both Sn and Tn excitons for radiative transitions, achieving 100% IQE without the need for rare earth metal phosphorescent complexes. Additionally, traditional fluorescent materials often experience energy dissipation and quenching, known as aggregation-induced quenching, in the aggregated state due to intermolecular collisions[9,10]. This characteristic significantly restricts the application scope of conventional fluorescent materials. It was not until Tang et al.[11] discovered a class of fluorescent materials with aggregation-induced emission (AIE) properties, which exhibit strong fluorescence only in the aggregated state. The restriction of intramolecular rotation and vibration in the aggregated state is identified as the main mechanism of AIE[12].
The photoelectric properties of organic luminescent materials are closely related to their molecular structure and intermolecular interactions, and they usually possess large conjugated structures. As a fundamental rigid conjugated unit lying between large π-conjugation and C=X (X being any bonding atom), the benzene ring features high stability, simple structure, and a direct relationship between its structure and properties, making it the optimal model compound for studying the excited-state properties of luminophores. However, at room temperature, benzene is a liquid and only becomes solid under harsh low-temperature conditions. If the benzene ring can be fixed into various heteroatom-containing, environment-responsive frameworks, extensive studies on its condensed-state structure and excited-state properties could be carried out, addressing the significant scientific issue of the luminescence mechanism of phenyl luminophores in different aggregation states. This paper first summarizes typical methods of chemical modification of the benzene ring in recent years. As shown in Figure 1, these include heterocycles, expansion of benzene ring conjugation, substitution of heteroatoms around the benzene ring, bridging between benzene rings, and other combination strategies. Based on this, the research progress of multifunctional organic luminescent materials constructed using these modification methods, such as fluorescent materials, phosphorescent materials from metal-organic complexes or clusters, TADF materials, unique AIE materials, and organic RTP materials, is reviewed.
图1 改性苯环的策略和基本结构示意图

Fig. 1 The concept diagram of phenyl derivatives mentioned in this review

2 Fluorescent Materials Based on Modified Benzene Rings

Organic fluorescent materials have received increasing attention due to their wide applications in biological sciences, fluorescent probes, clinical diagnostics, and OLEDs. Based on their structural characteristics, fluorescent materials can be divided into two categories: one is the π-extended conjugated system based on a rigid planar framework[13], and the other is the electron transfer system with a donor-π-acceptor structure[14⇓~16]. Due to effective intermolecular π-π stacking, the former suffers from severe fluorescence quenching at high concentrations and has low solubility in most organic solvents. In contrast, the donor-π-acceptor structure, consisting of relatively small conjugated systems, is widely used as the basic backbone for fluorescent materials and other optoelectronic materials. In recent years, monophenyl fluorophores have attracted considerable attention due to their small π-conjugated system and simple preparation, but there still lacks a straightforward strategy to modulate the photophysical properties of monophenyl fluorophores. To this end, Xiang et al.[17] developed a class of paraphenylenedinitrile-based fluorophores (1~8) with strong donor-acceptor structures to investigate the relationship between material chemical structure and photophysical properties (Figure 2). The simple monophenyl core and strong intramolecular charge transfer (ICT) enable these compounds to exhibit high fluorescence quantum yields, large Stokes shifts, and two-photon absorption. Additionally, by tuning the properties of the electron-donating groups, the emission wavelength of paraphenylenedinitrile derivatives can be easily adjusted from ultraviolet to near-infrared. Compared to the solution state, paraphenylenedinitrile derivatives show red-shifted emission in the solid state. Mechanistic studies reveal that dimer self-assembly in the solid state enhances ICT, leading to multi-emissive behavior in the solid. Notably, 3 exhibits highly crystalline and amorphous-dependent luminescence and reversible mechanochromic luminescence. Beppu[18] reported a new green fluorophore 9 (Figure 3). Based on efficient intramolecular hydrogen bonding and ICT, this compound shows high fluorescence intensity and photostability, with features such as solid-state luminescence, water solubility, and independence from solvent type and pH. The fluorescence quantum yield is 67%, and the Stokes shift is 140 nm. This structure differs significantly from traditional π-extended conjugated systems based on rigid planar molecular designs, providing a simple approach to green fluorescent materials containing a single benzene ring.
图2 1~8的化学结构和荧光发光波长[17]

Fig. 2 Chemical structure and fluorescence emission wavelength of 1~8[17]

图3 （a）9的化学结构；（b）在不同溶剂中的吸收和荧光光谱；（c）在水溶液和固态下的吸收和荧光光谱；（d）9在磷酸盐缓冲液中的摩尔消光系数（黑色）和荧光量子产率（红色）[18]

Fig. 3 (a) Chemical structure of 9. (b) Absorption and fluorescence spectra in different solvents. (c) Absorption and fluorescence spectra in aqueous and solid states. (d) 9 molar extinction coefficient (black) and fluorescence quantum yield (red) in phosphate buffers [18]

In organic fluorescent materials, red emitters are typically composed of large π-conjugated systems and often suffer from severe fluorescence quenching in the solid state, with almost no emitters that emit red fluorescence and have a molecular weight below 250. Most emitters with a molecular weight below 500 and red emission exhibit very small Stokes shifts, leading to self-absorption issues, making them unsuitable for multicolor fluorescence imaging[14,19,20]. Designing small-molecule fluorophores to achieve red emission, especially for bioimaging, has always been a challenge[21]. There is an urgent need for low-molecular-weight and biologically non-toxic red emitters. Mandal et al.[22] reported the red-emitting small molecule mono-phenyl ortho-substituted 10 and the orange-emitting 11 (Figure 4). Most reported small-molecule red emitters show negligible Stokes and solvatochromic shifts, yet 10 exhibits a high Stokes shift of up to 225 nm, a solvatochromic shift greater than 170 nm, and an excited-state lifetime of 26 ns. Tang et al.[23] reported a series of structurally simple 2,5-bis(alkylamino)terephthalate derivatives 12~14 (Figure 5), which consist of a very small π-system and emit efficient red light in the crystal form. 12 has a molecular weight of 252, a maximum emission wavelength of 620 nm, and a fluorescence quantum yield of 40%, exhibiting bright red light. The unique luminescent properties of the 12 crystal mainly originate from the planarization of the backbone due to strong intramolecular hydrogen bonding and the negligible π-π interactions due to the small π-system. In addition, besides the efficient red light, the high crystallinity grown in a co-planar manner allows the 12 crystal to exhibit typical amplified spontaneous emission under pulsed laser excitation. Thus, highly efficient organic crystals with amplified spontaneous emission were constructed based on a simple molecular structure consisting of only a single phenyl. Kim et al.[24] used diacetylbenzene diamine to construct novel different isomers of simple phenyl-based fluorescent materials 15~17 (Figure 6), with only 15 and 17 being fluorescent. Notably, 17 has the lowest molecular weight and emits red light at 618 nm. By changing the substituents on the diacetylbenzene diamine, a series of single-phenyl fluorescent materials covering the entire visible spectrum can be obtained. Theoretical analysis shows that their large Stokes shifts originate from the excited-state anti-aromaticity rather than ICT or proton transfer. The subtle interplay between excited-state anti-aromaticity and hydrogen bonding determines the photophysical properties of this new type of single-phenyl fluorophore, and extended π-conjugation is no longer a prerequisite for long-wavelength emission.
图4 （a）10和11的化学结构；10在不同溶剂中的（b）紫外照射图（c）发光光谱和（d）最大吸收，最大发光和斯托克斯位移[22]

Fig. 4 (a) Chemical structure of 10 and 11. 10 in different solvents (b) ultraviolet irradiation pattern, (c) emission spectrum and (d) maximum absorption, maximum emission and Stokes shift[22]

图5 （a）12~14的化学结构（最大发光波长和荧光量子产率）；（b）12晶体的发光照片和荧光光谱[23]

Fig. 5 (a) Chemical structure of 12~14 (maximum emission wavelength and fluorescence quantum yields). (b) Luminescent photographs and fluorescence spectra of 12 in crystal state[23]

图6 （a）15~17的化学结构和荧光量子产率；（b）在氯仿（50 μM）中的吸收和归一化发光光谱；插图比较了15和17的吸收和发光光谱；（c）17衍生物的化学结构（上）和归一化发光光谱（下）[24]

Fig. 6 Chemical structure and fluorescence quantum yields of 15~17. (b) Absorption and normalized emission spectra in chloroform (50 μM). The absorption and emission spectra of 15 and 17 are compared. (c) Chemical structure of 17 derivatives (top) and normalized emission spectra (bottom) [24]

Some unconventional luminophores without obvious π-conjugated structures have attracted the attention of researchers, with visible light emission in the aggregated state referred to as clustering-triggered emission (CTE)[25], which can be attributed to the formation of through-space conjugation (TSC). TSC is typically caused by spatial electron delocalization between spatially adjacent heteroatoms or aromatic units[26]. In contrast, traditional research based on π-conjugation is relatively mature. For instance, how the length of π-bond conjugation in a conjugated system affects fluorescence efficiency[27] has been well studied. However, the relationship between chain length and TSC intensity in non-conjugated systems remains uncertain, and the changes in photophysical properties with increasing TSC intensity are also unknown. Therefore, revealing the impact of TSC intensity on CTE in non-conjugated systems holds significant theoretical and practical value. Diphenylmethane, which exhibits noticeable TSC between its two freely rotating benzene rings, is one of the smallest CTE groups in this structural series[28]. Diphenylmethane can also serve as a repeat unit for poly(phenylene methylene), exhibiting blue luminescence[29,30]. As shown in Figure 7, Wang et al.[31] reported several oligo-para-phenylene methylenes (18~22) of different chain lengths, and their fluorescence spectra in acetonitrile-water mixed solvents indicated that after the formation of high-melting aggregates, the emission wavelengths of the oligomers were larger, with the TSC emission peaks of longer chains 20~22 red-shifted compared to 18 and 19. In the solid state, the shorter chains 18 and 19 showed dual-emission, with 280 nm emission from isolated benzene rings and 350 nm emission corresponding to weak TSC of the diphenylmethane units. With increasing chain length, the longer chains 20~22 exhibited additional TSC-induced CTE around 440 nm. Among 20~22, 22 had the highest photoluminescence quantum yield (PLQY) of 40%. A detailed analysis of the excited-state geometries of multiple oligomers revealed that the long-wavelength CTE at about 440 nm in 20~22 originated from internal diphenylmethane segments with small dihedral angles. In all compounds of different chain lengths, the short-wavelength emissions around 350 nm were due to external diphenylmethane segments with larger dihedral angles. Overall, unlike traditional π-bond conjugated luminophores, whose emission wavelengths redshift with increasing backbone, the CTE performance of TSC-induced oligomers does not show a linear relationship with chain length. The emerging internal diphenylmethane segments with small dihedral angles are crucial for the generation of long-wavelength emissions in long chains. Simultaneously, the increased rigidity of longer chains also leads to higher PLQY. This work not only demonstrates a clear structure-property relationship for TSC-based CTE but also provides a non-conjugated strategy for designing new multifunctional luminophores.
图7 （a）18~22的化学结构；（b）非共轭链长度与TSC强度之间的关系[31]

Fig. 7 (a) Chemical structures of 18~22. (b) The relationship between unconjugated chain length and TSC strength [31]

3 Phosphorescent Materials of Metal-Organic Complexes or Clusters Based on Modified Benzene Rings

Compared to the maximum IQE of 25% for traditional organic fluorescent materials, phosphorescent materials based on noble metal complexes such as platinum and iridium can achieve 100% IQE, thereby realizing superior OLED luminescence performance[32]. Therefore, phosphorescent OLEDs have broad commercial application prospects. However, the longer excited state lifetimes of phosphorescent materials make the devices prone to exciton annihilation at high brightness, leading to severe efficiency roll-off[33,34]. To obtain highly efficient phosphorescent OLEDs, it is necessary to use materials with high phosphorescent quantum yields and short emission lifetimes[35⇓~37]. In principle, enhancing the ISC process from Sn to Tn is beneficial for improving the phosphorescent quantum yield and shortening the lifetime[38⇓~40].
Cyclic trinuclear complexes containing heavy metal atoms, such as Hg(I), Au(I), Ag(I), and Cu(I), can coordinate with organic aromatics through π-acid-base interactions and promote the phosphorescence of organic aromatics via an external heavy atom effect[41⇓~43]. Although there are related studies[41], they still have some distance from ideal OLED applications. In addition, the preparation of cyclic trinuclear-organic aromatic complexes is relatively difficult[41,42,44]. Zhang et al.[45] prepared four complexes composed of a Cu6L3 cage host and halobenzene ligands (Figure 8). As the SOC constants of the halobenzenes (fluorobenzene (23), chlorobenzene (24), bromobenzene (25), and iodobenzene (26)) increased to 272, 587, 2460, and 5060 cm−1 respectively, the phosphorescent quantum yields of the complexes increased from 12.6% to 74.3%, and the lifetimes decreased from 30.11 μs to 18.39 μs, providing possibilities for the application in phosphorescent OLEDs, achieving high phosphorescent quantum yields with microsecond lifetimes for the first time in the field of metal-organic supramolecular cages. The phosphorescent quantum yields of the complexes showed a good linear relationship with the atomic numbers of the halogen atoms on the benzene ring. Theoretical calculations indicated that the 26 ligand could greatly promote the ISC process, which was in good agreement with the experimental results. This work developed a new method to enhance the phosphorescent quantum yield and shorten the lifetime by simply changing the ligand molecule, offering a new direction for the preparation of high-performance OLEDs.
图8 卤代苯配体23~26的化学结构及通过封装卤代苯配体增强Cu6L3笼的磷光示意图[45]

Fig. 8 Chemical structures of halogenated benzene ligand 23~26 and phosphorescence enhancement of Cu6L3 cage by encapsulation of halogenated benzene ligand [45]

In the current research on circularly polarized phosphorescent materials, the crystallinity of chiral materials often leads to poor processability[46], feasible strategies to address this issue include doping chiral materials into amorphous polymers[47] or covalently linking chiral materials to polymers[48]. These polymers restrict the vibrational relaxation decay of the Tn state of phosphorescent materials and enhance phosphorescence[49]. However, the ambiguous aggregated states of phosphorescent materials in these amorphous forms usually lead to a loss of chirality, adversely affecting the overall performance of circularly polarized phosphorescence. To this end, Guang et al.[50] constructed a supramolecular polymer-based circularly polarized phosphorescent system (Fig. 9) using benzil monomers 27~30, enhancing the non-covalent complexation of the designed monomers by introducing double hydrogen bonds between adjacent amides, where the phosphorescence lifetime of 27 is 0.31 ms at 298 K and increases to 2.1 ms at 77 K. Two peripheral wedge-shaped alkyl chains provide the supramolecular polymer with inherent film-forming capability, thus eliminating the need for additional polymers. The obvious helical asymmetry induced by chiral supramolecular polymerization leads to enhanced circularly polarized phosphorescence compared to its counterpart without hydrogen bonding. Altering the position of the chiral center or introducing halogen bonds significantly affects the performance of circularly polarized phosphorescence. Incorporating platinum(II) phosphorescent emitters into the benzil-based supramolecular polymer induces chirality and promotes triplet resonance energy transfer, resulting in a shift from yellow to red in circularly polarized phosphorescence. In summary, chiral supramolecular polymerization is a novel and effective method for preparing circularly polarized phosphorescent materials.
图9 （a）27~30的化学结构；（b）苯基化合物手性超分子聚合产生圆偏振磷光的示意图[50]

Fig. 9 (a) Chemical structure of 27~30. (b) Schematic diagram of circular polarization phosphorescence produced by chiral supramolecular polymerization of phenyl compounds [50]

Self-assembly refers to the process by which basic structural units spontaneously organize into ordered structures[51]. In recent years, the self-assembly of organic molecules, metal nanoparticles, and ultra-small nanomaterials has rapidly developed[52⇓~54]. Due to their precise structure and flexible tunability, the controlled self-assembly of metal nanoclusters is an emerging research field[55,56]. Although isolated metal nanoclusters exhibit low quantum yields, their self-assembly leads to highly efficient and tunable luminescent properties[57]. The formation of self-assembled structures of metal nanoclusters is guided by the electronic charge and functional groups of the ligands[58]. The volume and position of substituents on the ligands are decisive factors for the self-assembly of metal nanoclusters. Therefore, it is necessary to conduct in-depth studies on the formation mechanisms of metal nanocluster structures. As shown in Figure 10, Kolay et al.[59] designed Cu7 nanoclusters into ordered structures, only changing the position of methyl groups on the dimethylbenzyl alcohol ligands (31~33) to modulate the morphology of the assembly structures. The interactions of chalcophilicity, π-π stacking, and Cu…H-C enable the Cu7 nanoclusters to self-assemble from rod-like to sheet-like and then to ribbon-like structures. Stronger interactions with the meta-methyl group ultimately form a ribbon-like structure covered by 33 of the Cu7 nanoclusters. The lifetime decay curves of the three assemblies all show tri-exponential decay, with room temperature phosphorescence lifetimes of 31, 32, and 33 being 0.35, 0.65, and 1.69 µs, respectively. Additionally, the red phosphorescence of the three metal complexes is closely related to the compactness and effective interactions of the assembled structures, with strong compactness and interactions also leading to the longest excited state lifetime for the ribbon-like structure 33. In-depth studies of bond interactions in self-assembled metal nanoclusters pave the way for designing ordered structures with potential applications in optoelectronics, catalysis, and bioimaging.
图10 （a）配体31、（d）32和（g）33的结构；杆状（b，c）、片状（e，f）和带状自组装体（h，i）的扫描电镜和透射电镜图像[59]

Fig. 10 Chemical structure of ligands (a) 31, (d) 32, and (g) 33. SEM and TEM images of rod (b, c), platelets (e, f), and ribbon self-assembler (h, i) [59]

4 TADF Materials Based on Modified Benzene Rings

So far, OLEDs based on TADF materials have achieved high external quantum efficiency (EQE), with blue and green OLEDs exceeding 37% EQE, and red OLEDs approaching 30%. The performance of TADF materials is influenced by multiple factors. To ensure a high RISC during the emission process, it is typically required that molecules have a sufficiently small energy gap (energy gap between S1 and T1, ΔEST) between S1 and T1, and effective separation of the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO/LUMO) levels is key to achieving a small ΔEST and efficient RISC[60]. In single-component molecules, the ICT effect is usually determined by the steric hindrance between donor-acceptor structures. To achieve a small ΔEST, highly twisted molecular structures are needed, which often require complex organic synthesis, constructing effective donor-acceptor structures through intracyclic heteroatom substitution of benzene rings, non-aromatic conjugation extension, and bridging. On the other hand, ICT between different components can achieve a small ΔEST while avoiding complex organic synthesis. In such systems, HOMO and LUMO are located on the donor and acceptor, respectively[61]. By mixing different components together in the form of single crystals[62] or cocrystals[63], ICT can be easily achieved, while suppressing the rotation and non-radiative transitions of excited state molecules[64], providing a more ideal platform for regulating structure-property relationships than single molecules. Crystal engineering offers an effective and flexible way to modulate ICT, promoting RISC, thereby enhancing the utilization of excitons.
trans-1,2-Diphenylethylene (34) is a promising Tn state exciton sensitizing material that can form RTP cocrystals through the peripheral heavy atom effect with 1,4-diiodo-2,3,5,6-tetrafluorobenzene[65]. 1,2,4,5-Tetracyanobenzene (35) is commonly used as an acceptor in charge-transfer type cocrystals[66,67]. As shown in Figure 11, Hu reported[68] a cocrystal with a small ΔEST assembled from 34 and 35. The cocrystal is yellow, with a PLQY of 13.77%, and the calculated ΔEST is only about 0.01 eV. Donor-acceptor interactions are the main driving force for cocrystal self-assembly, which helps to form a rigid three-dimensional network with effective intermolecular interactions. The rigidity of the crystalline state ICT is the primary reason for efficient RISC, and this system simultaneously utilizes Sn and Tn state excitons. For the first time, TADF was observed in a cocrystal, and this cocrystal strategy provides a new mechanism for enhancing exciton utilization.
图11 （a）34（上）和35（下）的化学结构；（b）共晶发光图片和PLQY；（c）共晶发光过程的能级图[68]

Fig. 11 (a) Chemical structures of 34 (top) and 35 (bottom). (b) Eutectic luminescence pictures and PLQY. (c) Energy level diagram of eutectic luminescence process [68]

In addition, the inclusion complexes of macrocycles and small molecules are also an effective strategy for constructing efficient TADF. Zhou et al.[69] used calix[3]acridine as a cyclic donor to encapsulate 1,2-dicyanobenzene (36) acceptor in the solid state, resulting in bright blue-green TADF cocrystals (Figure 12) due to the effective ICT between calix[3]acridine and 36. The S1 and T1 energy levels were estimated to be 2.770 and 2.756 eV, respectively, based on fluorescence and phosphorescence spectra at 77 K. The effective separation of HOMO and LUMO led to a minimal ΔEST (0.014 eV), which is conducive to efficient RISC for promoting TADF emission. Under nitrogen, the PLQY of the cocrystal reached up to 70%, with the delayed component accounting for 60%. The high PLQY is attributed to multiple non-covalent interactions within the crystal, which not only enhance ICT but also suppress non-radiative transitions by restricting molecular motion in the rigid crystal framework.
图12 36作为客体的共晶，有效的分子间电荷转移增强TADF示意图[69]

Fig. 12 36 as an acceptor for eutectic, effective intermolecular charge transfer enhances TADF schematic diagram[69]

As shown in Figure 3, hexaazabenzene includes pyridine (37), diazines, and triazines (41). According to the relative positions of nitrogen atoms, diazines can be divided into three different regioisomers: pyridazine (38), pyrimidine (39), and pyrazine (40). Azaheterocycles usually act as electron-withdrawing groups[70⇓~72]. Yoon et al.[73] used phenyl and 37 as different acceptor structures, and substituted carbazole and 3,9′-bicarbazole at the 2 and 5 positions, respectively, to synthesize two OLED hosts 42 and 43 (with the same electron donor) (Figure 14). Both hosts exhibited good thermal stability and high Tn levels. Under a nitrogen atmosphere, at room temperature, using a 30% by weight of 5-(5,9-dioxa-13b-bromonaphtho[3,2,1-de]anthracen-7-yl)-10,15-diphenyl-10,15-dihydro-5H-diindolo[3,2-a:3′,2′c]carbazole doped 42 and 43 films, the PLQYs were 99.6% and 95.5%, respectively. The device corresponding to the 43 doped film had an EQE of 22.7% and a long lifetime of 24 h. The device corresponding to the 42 doped film had a similar EQE but a shorter lifetime of only 12 h. In addition, after mixing 2,4-bis(dibenzo[b,d]furan-2-yl)-6-phenyl-1,3,5-triazine into the doped films, the lifetimes of the three-component doped film devices of 42 and 43 were increased to 31 and 41 h, respectively. The electroluminescence peaks of all devices were around 480 nm. The results indicate that carbazole-based materials containing a pyridine core have considerable potential for achieving highly efficient and long-lived blue OLED devices.
图13 37~41的化学结构

Fig. 13 Chemical structures of 37~41

图14 42和43的化学结构和双组分掺杂器件的寿命曲线[73]

Fig. 14 Chemical structures of 42, 43 and life curves of two-component doped devices [73]

Triazines and their derivatives are also widely used as electron acceptors[74⇓~76]. In 2019, Braveenth et al.[77] used 41 as the acceptor to synthesize two green TADF materials, 44 and 45, by introducing different acridine donors (Figure 15). The ΔEST calculated from the room temperature and 77 K emission spectra of a 20% 44-doped 5-(5-(2,4,6-triisopropylphenyl)pyridin-2-yl)-5-benzo[d][4,5]imidazo[2-a]imidazole film and a 30% 45-doped bis(diphenylphosphine oxide)dibenzofuran film were 0.03 eV and 0.05 eV, respectively, with delayed lifetimes of 10.32 µs and 10.37 µs, respectively. The 45-doped film showed a PLQY of 79.7% under nitrogen. Several green OLED devices were fabricated using different hosts and doping concentrations, and the device with 30% 45-doped bis(diphenylphosphine oxide)dibenzofuran as the emitting layer exhibited a current density of 62.8 cd/A and a maximum EQE of 27.3%.
图15 （a）44和45的化学结构；（b）器件结构[77]

Fig. 15 (a) Chemical structure of 44 and 45. (b) Device structure[77]

Pyrimidine, due to its unstable empty π orbitals and strong luminescence modifiability, is the most widely used nitrogen-containing heterocycle currently. When combined with carbazole, acridine, and phenoxazine fragments, it exhibits deep blue, blue or sky blue, and green luminescence[78]. Nakao et al.[79] developed three pyrimidine-based TADF materials 46~48 (Fig. 16) for high-performance OLEDs, and thoroughly investigated the influence of the relative position of nitrogen on their luminescent properties. Among them, the delayed fluorescence lifetimes of 10 wt% 46~48-doped bis(2-diphenylphosphinophenyl) ether oxide films were 178, 87, and 55 µs respectively, and the PLQYs of the doped films under nitrogen atmosphere were 61%, 81%, and 81% respectively. Changing the position of the nitrogen atom in the pyrimidine core from symmetrical to asymmetrical reduced the ΔEST value of 47 by approximately half compared to that of the 46-doped film. The EQE of a blue TADF device based on 48, prepared using a double emission layer, approached 25%.
图16 （a）46~48的化学结构；（b）器件结构图；（c）46、（d）47和（e）48在室温下的发光过程示意图[79]

Fig. 16 (a) Chemical structure of 46~48. (b) Device structure diagram. Schematic diagram of the luminescence process of (c) 46, (d) 47 and (e) 48 at room temperature [79]

The research on pyrazine-based TADF materials is less than that of pyrimidines, and they are often used in conjunction with donors such as carbazole. Makhseed et al[80] reported a series of polycyanosubstituted pyrazine derivatives[80]49~51 (Figure 17). When doped into bis(2-diphenylphosphinophenyl) ether oxide films at a mass fraction of 10%, all three compounds exhibited TADF luminescence. Their spatial configurations help to suppress interactions, thereby stabilizing the emission color. As the number of carbazoles increased, the ΔEST, delayed fluorescence lifetime, and PLQY of 49, 50, and 51 doped films increased, from 0.15 eV, 4 µs, and 11% to 0.29 eV, 99.2 µs, and 24%, and then to 0.34 eV, 174 µs, and 36%. As shown in Figure 18, Kato et al[81] reported two pyrazine-based TADF materials 52 and 53. The PLQY of the film doped with 10% mass fraction of 52 in bis(2-diphenylphosphinophenyl) ether was 48%. The PLQY of the film doped with 10% mass fraction of 53 in 4,4′-bis(N-carbazolyl)-1,1′-biphenyl was 65%. The delayed fluorescence lifetimes of the 52 and 53 doped films were 134 and 54 µs, respectively. The ΔEST of the 52 and 53 doped films were 0.36 and 0.21 eV, respectively. The maximum EQE of the sky-blue OLED device based on 52 was 12%. The maximum EQE of the green OLED based on 53 was 21.4%.
图17 49~51的化学结构[80]

Fig. 17 Chemical structure of 49~51[80]

图18 （a）52和53的化学结构；（b）EQE-亮度曲线，插图： 0.1 mA时的电致发光光谱[81]

Fig. 18 (a) Chemical structures of 52 and 53. (b) EQE-luminance curve, illustration: electroluminescence spectrum at 0.1 mA[81]

Among all azabenzene derivatives, pyridazine has been rarely studied, and there were no reports on the application of pyridazine-based TADF materials in OLEDs before 2020. It was not until Krotkus et al[82] designed three molecules 54~56 containing pyridazine acceptors (Figure 19). In toluene solution, the molecules 54 and 55, with 9,9-dimethyl-9,10-dihydroacridine and carbazole as donors, exhibited blue-green and blue fluorescence, respectively, while 56, which has a strong electron donor phenoxazine, emitted green light, with a solution PLQY of 8.5% and a delayed luminescence lifetime of 470 ns under nitrogen atmosphere, attributed to effective TADF characteristics. The film doped with 15 wt% 56 in bis(2-diphenylphosphinophenyl) ether oxide had a PLQY of 13% measured under nitrogen atmosphere, and the calculated ΔEST was 0.086 eV. A green OLED fabricated using this as the emission layer achieved a maximum EQE of 5.8%.
图19 （a）54~56 的化学结构；（b）吡啶基发光体54（左）和56（右）在紫外光下的薄膜发光；（c）基于56器件的电致发光曲线，插图为点亮后的照片[82]

Fig. 19 (a) Chemical structures of 54~56. (b) 54 (left) and 56 (right) emit light in thin films under ultraviolet light. (c) electroluminescence curves based on 56 devices, illustrated by the illuminated photo [82]

Benzophenone57is a bridged derivative composed of a carbonyl group and two phenyl rings (Figure 20), often used as an acceptor unit in the synthesis of TADF materials due to its strong electron-withdrawing ability[83,84]. Additionally, xanthone58and acridanone59, which are obtained by modifying benzophenone with heteroatoms such as O and N as bridge groups, are also common electron acceptors for constructing TADF. Tang et al.[85]modified the rigid 58at the 3rd and 6th positions[83,86]with two acridine derivatives, synthesizing two green and blue TADF materials (Figure 21)60and61. These materials exhibit pronounced aggregation-enhanced delayed fluorescence. The configuration where the acceptor is orthogonally connected to a bulky donor not only facilitates the separation of HOMO and LUMO but also effectively suppresses tight molecular packing. The pure films of 60and61show PLQYs as high as 96% and 94%, respectively, under room temperature nitrogen conditions, with estimated ΔE STvalues from the fluorescence and phosphorescence spectra at 77 K being 0.025 and 0.024 eV, respectively. Due to restricted intramolecular motion, the PLQY and delayed fluorescence lifetime of the pure films of 60and61are significantly higher than those in polar tetrahydrofuran or nonpolar toluene solutions. The maximum EQE of OLED devices based on these two materials is around 24%. The undoped green OLED based on 60achieves a maximum EQE of up to 21%, showing minimal efficiency roll-off at 1000, 5000, and 10000 cd/m2, specifically 0%, 4.8%, and 14.3%, respectively. The undoped sky-blue OLED based on 61also achieves a maximum EQE of 21%, representing the most efficient sky-blue emission reported so far for undoped OLEDs. Furthermore, the doped OLEDs based on 60and61exhibit maximum EQEs of 25% and 27%, respectively, with efficiency roll-offs of 8.0% and 3.7% at 1000 cd/m2. These results indicate that whether undoped or doped, TADF devices based on 60and61have small efficiency roll-offs.
图20 57~59和63的化学结构

Fig. 20 Chemical structures of 57~59 and 63

图21 （a）60和61的化学结构；（b）基于60和61制备的掺杂器件及其EQE与亮度关系图[85]

Fig. 21 (a) Chemical structures of 60 and 61. (b) Doped device structures based on 60 and 61 and their EQE-luminance relationships[85]

59 and 58 have similar chemical structures and spatial configurations (Figure 20), which can be easily chemically modified with various groups[87,88]. In 2019, Siddiqui et al. [89] substituted carbazole at the 2nd and 7th positions of 59, preparing a green TADF material 62 (Figure 22). The ΔEST was estimated to be 0.17 eV from the low-temperature fluorescence and phosphorescence spectra in 2-methyltetrahydrofuran, and its PLQY in dichloromethane solution was 44%. Under nitrogen, the delayed fluorescence lifetime of 62 in acetonitrile solution reached 446 μs. The non-doped OLED prepared based on 62 had a startup voltage of 8 V, and at a current density of 25 mA/cm2, the luminous intensity was 1.25×103 cd/m2; electroluminescence peaks for the non-doped OLED based on 62 and the 62-doped OLED with 1,2-polyvinylcarbazole were observed at 505 and 465 nm, respectively. Before and after doping 62, the emission color of the device changed from green to cyan.
图22 （a）62的化学结构；（b）基于62的掺杂（左）和未掺杂（右）OLED发光照片[89]

Fig. 22 (a) Chemical structure of 62. (b) 62-based doped (left) and undoped (right) OLED luminescence photos[89]

Diphenylsulfone63, with the significant electronegativity of oxygen and the limited conjugation of the tetrahedral structure of the compound, has become a common acceptor for constructing TADF materials in recent years (Figure 20). Adachi et al. [90]have reported some TADF characteristics of compounds based on 63. The molecule 64obtained by substituting 3,6-di-tert-butylcarbazole at the 3, 6 positions of 63(Figure 23) showed excellent performance in doped OLED devices, achieving a maximum EQE of 9.9% and deep blue emission with CIE coordinates of (0.15, 0.07). To further adjust the electronic properties, the Su group [91]synthesized two different configurational bis(phenylsulfonyl)benzene isomers as blue TADF materials, 65and 66, by inserting a phenylsulfone into the 63unit (Figure 23). Calculations show that the introduction of the disulfonyl groups led to smaller ΔE STfor 65and 66compared to 64, at 0.19 and 0.26 eV, respectively. The PLQYs of the films doped with 10 wt% 65and 66in bis(2-diphenylphosphinophenyl) ether were 66.6% and 71%, respectively. The doped OLED device based on 66showed deep blue electroluminescence with CIE coordinates of (0.15, 0.08) and a maximum EQE of 5.5%. The device based on 65had better device efficiency, with a maximum EQE of 11.7%; due to the strong ICT effect of 65, its electroluminescence was sky blue, with CIE coordinates of (0.18, 0.19). The electroluminescence spectrum of the OLED based on 65was red-shifted, but the device efficiency was significantly higher than that of its meta-isomer 66and 64. Compared to 63, TADF luminescent materials constructed based on bis(phenylsulfonyl)benzene further improved the performance of OLEDs.
图23 （a）64的化学结构；（b）65和66的化学结构；基于65和66掺杂器件的（c）EQE与电流密度特性曲线和（d）电致发光光谱[90,91]

Fig. 23 (a) Chemical structure of 64. (b) Chemical structures of 65 and 66. (c) EQE and current density characteristic curves and (d) electroluminescence spectra based on 65 and 66 doped devices [90,91]

Compared to blue-to-orange TADF materials, the research progress on red TADF materials has been relatively slow. The main reasons are threefold: First, a small ΔEST between the S1 and T1 excited states is a fundamental characteristic of TADF materials, which contradicts the higher fluorescence radiative rate in single molecules of red TADF materials. Second, according to the energy gap law[92], as the emission wavelength shifts towards the red, non-radiative transitions dominate, leading to a decrease in PLQY. Third, many red emitters with highly conjugated extended features tend to form π-π stacking in the solid state, causing significant fluorescence quenching. Based on this, Wu et al.[93] synthesized three donor-acceptor-donor structured fluorescent molecules 67~69 using 2,1,3-benzothiadiazole as the acceptor (Figure 24). Theoretical calculations yielded ΔEST values of 0.69, 0.69, and 0.02 eV for 67~69. The PLQYs of pure films of 67 and 68 at room temperature were 27% and 54%, respectively, while the PLQY of a 3 wt% 69-doped film in 4,4'-di(9-carbazolyl)biphenyl was 56%. A red OLED with a doped 69 film as the emitting layer had an emission peak at 636 nm, with CIE coordinates of (0.61, 0.39). This device achieved a maximum brightness of 2980 cd/m2 at 11.2 V, a maximum current efficiency of 11.0 cd/A, and a maximum power efficiency of 10.8 lm/W. The maximum EQE of the red OLED device reached 8.8%.
图24 （a）67~69的化学结构；（b）基于69的OLED器件的EQE-亮度曲线（插图：器件结构和电致发光光谱）[93]

Fig. 24 (a) Chemical structures of 67~69. (b) EQE-luminance curves for 69-based devices (illustration: Device structure and electroluminescence spectra) [93]

Similar to small molecules, TADF polymers can also be constructed through donor-acceptor structures[94,95], but this requires precise adjustment of the positions between electron donors and acceptors to reduce ΔEST, which is not easy to achieve. Another strategy is to introduce small molecule TADF materials into the main chain or side chains of the polymer host[96,97]. This design is often difficult to realize due to the low T1 state energy level of the polymer host, especially for blue TADF units with high T1 state energy levels[98⇓~100]. Liu et al.[101] synthesized a new class of TADF polymers 70~72 (Figure 25) using carbazole and tetramethylphenyl as the backbone, 3,6-diphenylacridine as the donor, and 63, 57, or n-phenylnaphthalimide as the acceptor. By changing the electron-withdrawing ability of the acceptor, the charge transfer on the side chains gradually increased, resulting in maximum emission wavelengths of 486, 519, and 624 nm for the pure films. In addition, the calculated ΔEST for 70~72 were 0.01, 0.006, and 0.007 eV, respectively, enabling them to achieve efficient delayed fluorescence. The delayed lifetimes of the pure films of 70~72 under argon atmosphere were 27.4, 1.4, and 2.3 μs, and their PLQYs were 44%, 65%, and 5%, respectively. The PLQYs of 1,3-bis(N-carbazolyl)benzene doped with 70~72 were 74%, 84%, and 14%, respectively, and the corresponding OLEDs exhibited sky-blue, green, and red electroluminescence with maximum EQEs of 12.5%, 16.5%, and 3.6%, respectively. This study not only obtained red light TADF materials but also demonstrated the feasibility of color tuning for TADF polymers with carbazole and tetramethylphenyl as the backbone.
图25 （a）70~72的化学结构；（b）聚合物纯膜的稳态PL光谱[101]

Fig. 25 (a) Chemical structures of 70~72. (b) Steady-state PL spectra of polymer pure films [101]

Most OLEDs emit in the visible light region[102], while near-infrared TADF materials with a maximum emission peak exceeding 700 nm are rare[103,104]. Although some near-infrared TADF materials have high fluorescence quantum yields, their device performance is far behind that of visible-light TADF OLEDs[105,106]. In 2020, Kumsampao et al.[107] used a highly electron-deficient 5,6-dicyano[2,1,3]benzothiadiazole as a strong electron acceptor to provide the strong donor-acceptor interaction required for near-infrared emission. A highly efficient donor-acceptor-donor type near-infrared TADF material 73 (Figure 26) was synthesized by capping with triphenylamine units as electron donors, with a calculated ΔEST of 0.07 eV. The transient lifetime of a 30% doped film of 73 in 4,4'-di(9-carbazolyl)biphenyl under oxygen-free conditions at room temperature was 7 ns, and the delayed lifetime was 1.52 µs, with a PLQY of 52%. The PLQY in toluene solution was 70%. The doped OLED based on 73 exhibited a maximum EQE of 6.57% and a maximum electroluminescence wavelength of 712 nm. This result provides a simple strategy for constructing near-infrared TADF materials and indicates that 73 is a low-bandgap strong electron acceptor for use in OLEDs.
图26 73的化学结构与近红外发光的图片和光谱[107]

Fig. 26 Chemical structure of 73, image and spectrogram of near-infrared emission[107]

OLEDs with both high efficiency and narrowband emission characteristics are becoming increasingly important for energy saving and high-quality displays. The inherent ICT characteristics of donor-acceptor structures can be offset by strong intramolecular or intermolecular interactions, leading to a redshift in emission, which makes it very difficult to achieve deep blue TADF emission[103]. OLEDs based on multi-resonance induced TADF materials have great potential in achieving efficient and narrowband deep blue OLEDs[108,109]. This molecular structure triggers the alternating distribution of HOMO and LUMO in the aromatic skeleton according to the resonance effect, enabling the molecule to have a small ΔEST and large emission oscillator strength, thus achieving efficient and narrowband TADF emission. However, during high-brightness operation of OLEDs, efficiency roll-off due to the slow RISC process hinders the expansion of multi-resonance induced TADF materials in practical applications. As shown in Figure 27, Hu et al.[110] reported two multi-resonance induced TADF materials containing heavy atom selenium (74 and 75). The PLQY of films doped with 1% mass fraction of 74 and 75 in 1,3-dihydro-1,1-dimethyl-3-(3-(4,6-d-phenyl-1,3,5-triazine-2-yl)phenyl)indeno[2,1-b]carbazole were 99% and 100%, respectively, with delayed fluorescence lifetimes of 12.7 and 9.9 μs, and RISC rates calculated from experimental values of 0.6×106 and 2.0×106 s−1. The green light OLED based on 75 exhibited a maximum EQE of up to 36.8% at high brightness and ultra-low roll-off (roll-off values of 2.8% and 14.9% at 1000 and 10,000 cd/m2, respectively). The performance of the OLED corresponding to 74 was relatively lower but still reached a maximum EQE of 35.7% with a smaller efficiency roll-off (a roll-off value of 10.4% at 1,000 cd/m2). In addition, the excellent Tn exciton trapping capability of 75 also made it an efficient OLED sensitizer, with the OLED based on this having an EQE as high as 40.5%, a luminance close to 20,000 cd/m2, and excellent luminescence properties. The results indicate that a strong heavy atom effect can effectively promote the RISC process of multi-resonance induced TADF materials while maintaining high PLQY and narrowband emission. This work provides new ideas for the design of multi-resonance induced TADF material light-emitting devices and efficient OLED sensitizers. Jin et al.[111] synthesized two asymmetric multi-resonance induced TADF materials 76 and 77, and combined the two compounds into 78 (Figure 27). In toluene solution, 78 had the highest PLQY of 93% among the three compounds, a half-width of 26 nm, and a RISC rate of 2.1×104 s−1. The PLQY and half-width of 76 and 77 were 85%, 90%, and 30, 29 nm, respectively. Without using any TADF sensitizer, the simple three-layer structure doped OLED device based on 78 achieved a maximum EQE of 24.15% with CIE coordinates of (0.15, 0.10), which is one of the best efficiencies reported for deep blue OLEDs. The results show that extended multi-resonance TADF emitters have higher efficiency and bluer, narrower emissions.
图27 74~78的化学结构[110,111]

Fig. 27 Chemical structures of 74~78[110,111]

5 AIE Materials Based on Modified Benzene Rings

So far, AIE luminescent materials, as a class of striking materials, have been widely applied in fields such as OLEDs, optical waveguides, photovoltaics, biosensors, bioimaging, and drug delivery[112⇓⇓~115]. AIE molecules typically possess flexible twisted conformations and rotatable (vibrational) parts, thereby restricting the free movement of the molecules in space in the aggregated state, which suppresses the non-radiative transitions of the excited state energy, thus exhibiting enhanced radiative luminescence intensity[116].
In recent years, a new class of propeller-shaped luminescent molecules with AIE behavior has emerged, which typically exhibit large Stokes shifts due to significant changes in the excited-state conformation[117,118]. Additionally, compared to traditional planar π-conjugated luminophores, the luminescence of twisted AIE luminogens can be attributed to effective TSC between different subunits. Scientists have discovered some special non-conjugated AIE luminogens that possess more flexible conformations and stronger TSC than conjugated systems[119⇓~121]. Therefore, this intrinsic property of non-conjugated luminophores may provide the possibility of manipulating the excited-state processes through the parity effect. Xiong et al.[122] designed a series of non-conjugated tetraphenylalkanes 79~85 with varying alkyl chain lengths from methane to heptane (Figure 28). It was found that these tetraphenylalkanes exhibited a surprising excited-state parity effect, determined by three factors: the geometry of the alkyl groups, molecular mobility, and intermolecular packing. In the powder state, tetraphenylalkanes with even-numbered alkyl carbons showed strong TSC, long-wavelength emission, and high PLQY of 43%~68%. However, those with odd-numbered alkyl carbons were almost non-luminescent, with PLQY all below 9%. These tetraphenyl luminescent alkanes, with their flexible conformations, were successfully used for fluorescent information encryption.
图28 79~85的化学结构及发光照片[122]

Fig. 28 Chemical structures and luminescences of 79~85[122]

Light-excited controllable AIE can be carried out in a single solvent, thus opening up new avenues for the preparation and processing of smart materials. Compared with traditional AIE, strategies for light-excitation controlled AIE[123,124]urgently need further development to achieve precise remote control over a single medium. Because it is easy to exacerbate side reactions such as photo-oxidation[117,121,125], applying light-excitation controlled AIE in organic phases remains a challenge. Considering that research on light-excitation controlled materials is still at an early stage[126⇓~128], as shown in Figure 29, Zhu et al.[129]selected typical polysulfurated aromatics 86as a prototype to explore the impact of molecular conformation on the ground state and excited state. Theoretical calculations showed that there was a significant change in the spatial conformation of 86from the ground state to the excited state. As the light exposure time increased, the molecules in dichloromethane gradually changed from non-luminescent to cyan, with the luminescence intensity at 470 nm gradually increasing, indicating aggregation. Dynamic light scattering and transmission electron microscopy images showed that the particle size gradually increased from a few nanometers to hundreds of nanometers. With the increase in solvent polarity, the emission peak shifted from 470 nm to 530 nm, and the color changed from cyan to green. However, the molecule suffers from an unfavorable photo-oxidation process, which affects the reversibility of the light-induced aggregation. To avoid this photo-oxidation and improve the efficiency of light-induced aggregation, environmental factors affecting the molecule were optimized. By reducing UV light intensity, removing oxygen, and increasing solvent polarity, the efficiency of light-induced aggregation was improved.
图29 （a）86在光激发下的化学结构和构象；（b）0~120 s和（c）120~360 s光照射下86在二氯甲烷中的光谱变化；（d）光照射后溶剂极性变化的CIE及相应照片；（e）弱紫外灯（365 nm, 4 W）下二氯甲烷中的光谱变化；（f）氩气气氛下脱气二氯甲烷中的光谱变化（365 nm, 5 W）[129]

Fig. 29 (a) Chemical structure and conformation of 86 under photoexcitation. Spectral changes of 86 in dichloromethane under (b) 0~120 s and (c) 120~360 s light irradiation. (d) CIE and corresponding photos of solvent polarity changes after light irradiation. (e) The spectral change of dichloromethane under weak ultraviolet lamp (365 nm, 4 W). (f) Spectral changes of degassed dichloromethane under argon atmosphere (365 nm, 5 W) [129]

A series of AIE fluorescent water sensors have been reported, especially those based on tetraphenylethylene AIE materials, which exhibit excellent detection performance[130⇓⇓~133]. On the other hand, triphenylamine, as a strong electron donor, when covalently linked with electron-withdrawing groups, can result in donor-acceptor structures with significant ICT or twisted intramolecular charge transfer (TICT) effects. At the same time, the non-planar propeller-like molecular structure of triphenylamine can effectively prevent intermolecular π-π stacking, thereby inhibiting fluorescence quenching. Therefore, triphenylamine is also an ideal unit for constructing various AIE materials[134⇓⇓~137]. Triphenylamine has stronger electron-donating ability than tetraphenylethylene, and AIE molecules based on triphenylamine are more sensitive to external stimuli. However, there are few reports on AIE-active fluorescent probes based on triphenylamine for water detection[137,138]. Ruan[139] synthesized a simple triphenylamine-based compound 87 through a one-step Friedel-Crafts acylation reaction. The twisted molecular conformation of 87 endows it with effective TICT and excellent AIE properties (Figure 30). In addition, 87 exhibits significant solvatochromic characteristics and extremely high sensitivity to water in organic solvents. The detection limits for water in tetrahydrofuran and 1,4-dioxane are as low as 76 ppm (volume fraction of 0.0068%, 1 ppm=1×10-6) and 31 ppm (volume fraction of 0.0032%), respectively. In the presence of trace amounts of water, the probe can distinguish the water content in organic solvents, and a significant change in fluorescence color can be observed by the naked eye. As the water content increases from 0% to 6%, the fluorescence color of the 87 solution gradually changes from deep blue to sky blue, then to green, and finally to dark green. The low detection limit and significant fluorescence color change make it an ultra-sensitive water detector for organic solvents.
图30 87的化学结构、AIE和TICT性质及其对水（体积%）的肉眼荧光检测[139]

Fig. 30 Chemical structure, AIE and TICT properties of 87 and their macroscopic fluorescence detection of water (vol%)[139]

6 Pure Organic RTP Materials Based on Modified Benzene Rings

Unlike metal complex-based RTP materials, the radiative transitions of excitons in purely organic RTP materials cannot compete with non-radiative transitions due to the presence of ineffective ISC[140], making the design of highly efficient and long-lived purely organic RTP materials extremely challenging. It is generally believed that two factors are key to achieving RTP luminescence: one is promoting effective ISC to obtain Tn state excitons, and the other is suppressing non-radiative transitions[141]. ISC is primarily determined by SOC and ΔEST. Heavy atoms or heteroatoms can be introduced to enhance SOC, thereby promoting ISC and increasing phosphorescence quantum yield[142,143]. Additionally, introducing hydrogen bonds can rigidify molecular conformations, reducing non-radiative transitions of Tn excitons, thus achieving ultra-long lifetimes and high efficiency[144,145]. SOC can also be enhanced through delocalization of hydrogen bonds, which strengthens molecular orbitals, thereby accelerating ISC and promoting phosphorescence generation[146,147]. Moreover, halogen bonds, which are a strong type of non-covalent interaction with stronger directionality compared to hydrogen bonds, are also beneficial for RTP. In summary, the performance of organic RTP materials is highly dependent on intermolecular interactions[148⇓~150]. Intermolecular interactions can promote electron delocalization between adjacent molecules, lowering the energy levels of luminescent materials. This section reviews the impact of different intermolecular interactions, such as π-π interactions, n-π interactions, halogen bonds, and hydrogen bonds, on the performance of purely organic RTP materials based on modified benzenes, as well as some organic RTP materials with unique applications.
As shown in Figure 31, Sasabe et al. [151] reported on organic RTP materials, halogenated derivatives of 3-pyridylcarbazole 88 to 92. The phenyl analog 93 of 91, due to the absence of a nitrogen atom on the central benzene ring, does not have intermolecular hydrogen bonds that restrict molecular motion in its crystals, thus it emits fluorescence. In contrast, the intermolecular interactions of 88 to 92 limit molecular motion, thereby suppressing non-radiative transitions. Theoretical calculations indicate that the presence of the pyridine ring enhances the SOC constant. By introducing different halogen atoms at the same position on the benzene ring, the derivatives also exhibit varying degrees of increase in SOC, with a larger SOC constant corresponding to a shorter phosphorescence lifetime. Among the studied derivatives, 89 has the longest single-crystal phosphorescence lifetime of 1.1 s and a phosphorescence quantum yield of 1.2%. The bromo-substituted derivative exhibits strong yellow emission with an emission peak wavelength of 546 nm, a single-crystal phosphorescence lifetime of 0.15 s, and a phosphorescence quantum yield of 7.9%. Chen et al. [152] investigated two simple aromatic acids: nicotinic acid 94 and isonicotinic acid 95 (Figure 32). These do not emit light in solution but show visible RTP in the crystalline state. In the crystals of 94 and 95, there are strong hydrogen bonds between the nitrogen atom of the pyridine and the carboxyl group, leading to zigzag and linear molecular packing for 94 and 95 respectively. Theoretical calculations confirm that these hydrogen bonds effectively promote the ISC process. The identical molecular orientation in the molecular packing results in a larger dipole moment for 95 compared to 94, which is the reason for the redshift in the emission and RTP of 95. When the hydrogen bonds are disrupted, the RTP performance significantly decreases, further confirming the crucial role of hydrogen bonds in RTP. The strong hydrogen bonding interaction between the pyridine nitrogen atom and the carboxyl group provides new insights into the molecular design of organic luminescent materials.
图31 （a）88~93的化学结构；（b）UV灯关闭前后的余辉[151]

Fig. 31 (a) chemical structure of 88~93. (b) Afterglow before and after UV lamp is turned off [151]

图32 （a）94和95的化学结构；（b）94和95的晶体堆积结构；（c）94和95晶体室温下的荧光和磷光光谱[152]

Fig. 32 (a) Chemical structures of 94 and 95. (b) The crystalline packing structure of 94 and 95. (c) Fluorescence and phosphorescence spectra of crystals 94 and 95 at room temperature[152]

Aryl ketones, due to their strong Tn exciton providing capability, are used as materials for achieving ultra-long-lived pure organic RTP [145]. According to the El-Sayed rule, the presence of lone pair electrons on oxygen atoms can promote the transition from n-π* to π-π* orbitals, thereby increasing the number of Tn excitons. Boron-containing aryl ketone compounds typically exhibit strong fluorescence and high-performance RTP [153,154]. However, due to the complex structure of these boron-containing materials in the solid state, the mechanism behind their ultra-long-lived phosphorescence is not yet understood. Therefore, Jin et al. [155] selected a series of 4-carbonyl phenylboronic acid derivatives 96~101 (Figure 33) to gain a deeper understanding of the relationship between the luminescent behavior of the selected compounds and their molecular structures as well as intermolecular interactions. The results showed that electron-donating groups have a positive impact on extending the phosphorescence lifetime of the materials. As the electron-donating ability increases, except for 101, the RTP lifetimes of the crystalline compounds 96~100 increase, being 11.69, 69.56, 295.04, 370.93, and 431.46 ms, respectively. On the other hand, multiple intermolecular π-π interactions are conducive to forming a stable rigid stacking structure, thereby restricting molecular vibrations and ultimately prolonging the phosphorescence lifetime. Additionally, 100 has the highest RTP efficiency, with its phosphorescence lifetime and phosphorescence quantum yield being 431 ms and 4.5%, respectively.
图33 （a）96~101的化学结构；（b）6种晶体的稳态和磷光光谱，在环境光下（左），365 nm紫外灯关闭前（中）和后（右）的晶体照片[155]

Fig. 33 (a) Chemical structure of 96~101. (b) Steady-state and phosphorescence spectra of six crystals, under ambient light (left), before (middle) and after (right) the 365 nm UV lamp is turned off [155]

Inspired by the strategy of co-doping with rare earth metals in inorganic luminescent materials[156], Zhou et al.[157] proposed a TADF-assisted Förster resonance energy transfer strategy, hypothesizing that continuous energy transfer from donor molecules to RTP materials would prolong the luminescence lifetime of RTP materials and produce ultra-long RTP. They designed a series of donor-acceptor type two-component crystals (see Figure 34). The triazine and amino groups of melamine donor 102 can promote TADF, while three isomers of phthalic acid, o-phthalic acid (103), m-phthalic acid (104), and p-phthalic acid (105), serve as acceptors[158]. Hydrogen bonding interactions between 102 and 103~105 facilitate the formation of two-component crystals. There exists efficient energy transfer between the donor and acceptor molecules, with an energy transfer efficiency as high as 76%. The highly symmetrical structure of 102 facilitates self-assembly in all directions with structurally similar aromatic acids, providing suitable orientation for effective energy transfer. The prepared cocrystalline materials 102+103, 102+104, and 102+105 all exhibit ultra-long RTP, with visible afterglow of different colors in the range of 0 to 20 seconds. The phosphorescence lifetime of 102+104 reaches up to 2 seconds, which is higher than most reported RTP materials. Shimizu et al.[159] reported 1,4-bis(aryl)-2,5-dibromobenzene derivatives 106~110, which do not emit light in solution or doped polymer films. However, the crystals exhibit phosphorescence under ambient conditions (see Figure 35). By changing the substituents on the benzene ring, the color of the crystal phosphorescence of 106 to 110 changes from blue to green. The PLQY of 106 to 110 crystals at room temperature is 5% to 18%, and at 77 K it is 38% to 67%. Better luminescence efficiency at lower temperatures indicates that intramolecular rigidity is a necessary condition for crystallization-induced RTP. In each crystal, intermolecular interactions such as C=O...H, Br...Br, C=O...Br, F...F, and S...H are observed, which restrict intramolecular motion, thereby weakening the non-radiative transition process of Tn excitons.
图34 （a）102~105的化学结构；（b）三种双组分晶体在365 nm UV灯关闭前后的余辉图片[157]

Fig. 34 (a) Chemical structures of 102~105. (b) Afterglow pictures of three two-component crystals before and after the 365 nm UV lamp is turned off [157]

图35 （a）106~110的化学结构；（b）室温下365 nm UV灯照射前后晶体图片[159]

Fig. 35 (a) Chemical structure of 106~110. (b) Crystal picture before and after 365 nm UV lamp irradiation at room temperature [159]

As mentioned earlier, most organic RTP materials generally have low ISC leading to low RTP efficiency. Solutions have focused on enhancing ICT with strong covalent bonds and three-dimensional structures[160]. However, the charge transfer through the bond is relatively insensitive to the environment, and the charge transfer of most traditional organic RTP materials does not respond to the introduced covalent bond. Zhu et al.[161] believe that single molecules relying on intramolecular non-covalent interactions can effectively solve this problem, proposing a pillararene RTP system responsive to alkyl halide guests. As shown in Figure 36, one phenyl ring of dimethoxypillar[5]arene is functionalized with meta-formylphenyl or para-formylphenyl 111 and 112, these derivatives support effective spatial charge transfer within the pillar-arene cavity. For 112, the spatial charge transfer occurs from the opposing 1,4-dimethoxybenzene units to the para-formylphenyl unit, producing two dark Sn states, allowing 112 to exhibit a single ISC channel between its dark S1 min and T1, showing weak luminescence and undetectable RTP. In contrast, 111 after optimizing the Sn state, two S1 min were found; 111 exhibits more possible ISC channels between an effective S1 min and T4, T3, and T1, reflecting good electronic communication pathways within the pillar[5]arene cavity. These channels include small energy gaps and identical transition configurations. In this case, a clearly visible S1 min and T1 due to significant vibrational relaxation can be observed, features that reflect the presence of complex yet rational spatial charge transfer within the pillar[5]arene cavity, thus generating efficient RTP. Studies using alkyl halides as guests show that pillar[5]arenes exhibit typical guest recognition, and alkyl halide guests containing heavy atoms can be used to modulate the photophysical characteristics of the system. The sensitivity of quantum yield and excited-state lifetime to the structure of alkyl halide guests allows 111 to play a crucial role in the detection and identification of halogenated volatile organic compounds.
图36 （a）111和112的化学结构和空间电荷转移特征；（b）111和112的能级图；（c）111和112的S1态和Tn态的能级在Sn态最小能级±0.3 eV范围内跃迁的概率[161]

Fig. 36 (a) Chemical structure and trough-space charge transfer characteristics of 111 and 112. (b) Energy level diagrams for 111 and 112. (c) The probability of transitions of the S1 and Tn states of 111 and 112 within the minimum Sn state level ± 0.3 eV [161]

Reports on red and near-infrared RTP are relatively limited[162,163], and compared to complex multi-component systems, single-molecule studies of red and near-infrared phosphorescence are the least explored[164⇓~166]. 1,3,5-trifluoro-2,4,6-triiodobenzene (113) and its analogs, as halogen donors, have been widely used in the construction of supramolecular materials[167,168], and their phosphorescent properties are modulated through the individual or synergistic effects of σ-holes and π-holes[169,170]. However, no one has studied their own luminescent properties. Liu et al.[171] conducted a detailed study of the phosphorescence and mechanism of 113 for the first time (Figure 37), proposing a new mechanism where iodine atoms act as chromophores promoting n-π* transitions, in addition to the heavy-atom effect. At the same time, σ-holes and π-holes in the crystalline state can stabilize Tn state excitons by confining n-electrons, thus slowing down the radiative rate of Tn excitons. In the crystalline state, 113 exhibits a phosphorescence quantum yield of 0.1% and a phosphorescence lifetime of 3.6 ms. This work is the first to investigate the near-infrared phosphorescence of the simple organic molecule 113, which holds significant implications for the synthesis of small-molecule long-wavelength phosphorescent materials.
图37 （a）113的化学结构、晶体发光和n-π*跃迁示意图；（b）113晶体近红外磷光中σ-空穴键捕获激发电子的机理[171]

Fig. 37 (a) Chemical structure of 113, crystal luminescence picture and n-π* transition diagram. (b) Mechanism of trapping excited electrons by σ-hole bonds in near-infrared phosphorescence of 113 crystals [171]

Benzothiadiazole is a commonly used acceptor material, and the heteroatoms help to emit phosphorescence from the lower energy Tn state[172], which is conducive to constructing red or near-infrared RTP materials. Matsumoto et al.[173] reported benzothiazole materials 114 containing methoxy and bromine atoms and their analogs 115 and 116. The three materials exhibit red RTP in the crystalline state (Fig. 38), and the relationship between phosphorescent properties and crystal packing structures was systematically studied. Taking 114 as an example, introducing methoxy and bromine atoms into the electron-accepting benzothiazole generates long-wavelength red phosphorescence. The heavy atom effect of the bromine atom accelerates ISC, producing Tn state excitons. Although these materials inherently possess phosphorescent characteristics in the monomer state, RTP in the crystalline state is achieved through various intermolecular interactions (such as π…π bonds, C—H…O bonds, and short contacts with Br atoms). Under ambient conditions at room temperature, the phosphorescence quantum yields of the crystals of 114~116 are 3.7%, 1.8%, and 1.6% respectively. The phosphorescence lifetimes are 585, 233, and 110 μs, respectively. This result provides a general strategy for achieving long-wavelength phosphorescence in single molecules. As shown in Fig. 39, Garain et al.[174] reported a simple phthalimide derivative 117. The presence of carbonyl and bromine atoms effectively enhances ISC and SOC between Sn and Tn, which plays a crucial role in achieving efficient phosphorescence under room temperature and air conditions. A film doped with 1% by mass of 117 in poly(methyl methacrylate) exhibits visible cyan afterglow to the naked eye, with a phosphorescence lifetime of 0.73 ms monitored at 500 nm, a phosphorescence quantum yield of 4% in air at room temperature, and 8.9% in vacuum. Notably, the doped film maintains phosphorescence behavior even after 20 days under ambient conditions at room temperature, demonstrating excellent air stability at room temperature. Additionally, increasing the doping concentration of 117 in the poly(methyl methacrylate) matrix reduces the emission intensity and lifetime, indicating that aggregation leads to phosphorescence quenching. In the crystalline state, it exhibits orange-red phosphorescence, with broad emission in the orange-red region observed after excitation at 350 nm, with a maximum emission at 616 nm and a phosphorescence lifetime of 15.7 ms.
图38 （a）114~116的化学结构；（b）晶体的余辉照片和磷光发光波长，荧光和磷光量子产率及磷光寿命[173]

Fig. 38 (a) Chemical structures of 114~116. (b) Afterglow photographs and phosphorescent emission wavelengths of crystals, fluorescence and phosphorescent quantum efficiency and phosphorescent lifetime [173]

图39 117的化学结构[174]

Fig. 39 Chemical structure of 117[174]

In addition to the simple phenyl monomolecular red-light RTP materials mentioned earlier, researchers have also turned their attention to polymers. Wu et al[175] used tetrafluoroterephthalic acid as a raw material to synthesize the monophenyl molecule 2,5-di(allylamino)-3,6-di(methylseleno)terephthalonitrile and copolymerized it with acrylamide to obtain 118 (Figure 40). The cyano group acts as an electron donor, while the tertiary amine group serves as an electron acceptor. 118 exhibits maximum fluorescence emission at 541 nm and shows red RTP with an emission wavelength of 605 nm under 405 nm excitation, with a lifetime of 1.57 ms and a large Stokes shift of 200 nm. Notably, 118 displays excitation wavelength-dependent luminescence. Theoretical calculations indicate that selenium atoms can enhance SOC and promote the ISC process. This result provides a feasible and simple strategy for constructing long-wavelength-emitting RTP materials in polymers.
图40 （a）118的化学结构；（b）118的堆积结构和发光示意图[175]

Fig. 40 (a) Chemical structure of 118. (b) Schematic diagram of the stacking structure and luminescence of 118[175]

The application of pure organic RTP materials in bioimaging and sensing is typically achieved by suppressing molecular motion in the crystalline state[7,148,176⇓~178], or by embedding them in a polymer matrix to suppress vibration and oxygen-induced triplet non-radiative quenching[179⇓~181]. The next challenge in this field is to achieve efficient RTP in solution and gel phases, as most of the solution-state phosphorescent materials reported so far exhibit lower quantum yields compared to their crystalline or film states[182⇓~184]. Although Liu et al. [165] reported a phosphorescence quantum yield as high as 99.83% for luminophores and cucurbit[8]uril doped films using a "supramolecular pinning" strategy, the phosphorescence quantum yield of the corresponding luminophores and cucurbit[8]uril aqueous solutions was only 12.1%. Therefore, the further development of solution-state luminophores requires improving their efficiency under ambient aerobic conditions. Garain et al. [185] reported a simple heavy-atom-substituted cationic o-phenylenediamine derivative 119 (Figure 41). An attempt to achieve RTP luminescence in an aqueous solution through 1:1 host-guest complexation of 119 with cucurbit[7]uril resulted in a phosphorescence lifetime of 104 ms and a phosphorescence quantum yield of 6%. To further enhance the phosphorescence efficiency of 119, a supramolecular anchoring approach was used, where the negatively charged surface of laponite (LP) nanoclay served as a template to anchor the cations. As the concentration of 119 increased, the negative charge of LP decreased, indicating the presence of hybrid co-assembly. With an increase in the mass fraction of LP (0.125% to 6%), titration of the 119 aqueous solution (0.5 mmol/L) gradually showed strong cyan phosphorescence. When the LP mass fraction reached 6%, the phosphorescence efficiency was strongest, with a room-temperature phosphorescence quantum yield of 41.8%, and the solution viscosity was relatively high. Based on this, further addition of 10% mass fraction of LP to form a phosphorescent hydrogel with 119 displayed a cyan phosphorescence of 1.34 ms and a phosphorescence quantum yield of 34.2%. By adding certain proportions of sulfonamide G and sulfonamide 101 dyes, the LP-119 complex could be further used as an efficient donor scaffold. Orthogonal anchoring acceptors were realized through effective Förster resonance energy transfer from Tn to Sn, which is rarely achieved in solution. The resulting yellow and orange hydrogels exhibited delayed fluorescence, with lifetimes of 162 and 55 ms, and PLQYs of 81% and 37%, respectively. This study will guide future research on solution-state phosphorescent materials and their applications in imaging and sensing in biological systems.
图41 （a）119、葫芦[7]脲和LP的化学结构；（b）上：LP- 119络合物的相互作用示意图、LP-119络合物到磺胺G的Förster能量转移示意图和发光光谱及其发光图片；下：使用LP-119络合物和加入磺胺G和磺胺101后的水凝胶254 nm紫外光下书写“NCU”照片[185]

Fig. 41 (a) Chemical structures of 119, cucurbit[7]uril and LP. (b) Above: Interaction diagram of LP-119 complex, Forster energy transfer diagram of LP-119 complex to sulfanilamide G, luminescence spectrum and luminescence picture. Next: Write "NCU" photos under 254 nm UV light using LP-119 complex and hydrogel with sulfanilamide G and sulfanilamide 101 added [185]

The application of organic RTP materials in bioimaging and sensing in aqueous environments is often limited by phosphorescence quenching caused by water components. Water-induced enhanced RTP can overcome this limitation, but the underlying mechanisms are still unclear. Xu et al.[186] selected tricarbolic acid 120 as the host and tricarboxylic acid 121 as the guest to obtain doped powder P1 (Figure 42), which exhibited a phosphorescence lifetime of 1.13 s and a phosphorescence quantum yield of 9.3% at room temperature. When 20 wt% water was added to P1, the resulting powder P1W showed a significant increase in both phosphorescence lifetime and efficiency, with a phosphorescence quantum yield and lifetime of up to 46.1% and 1.67 s, respectively, at room temperature. The active host activates Tn excitons through Dexter energy transfer to achieve strong phosphorescence, and utilizes hydrogen bonds from water to harden the matrix to suppress non-radiative transitions, thereby achieving efficient luminescence. This provides a general approach for designing strongly luminescent and highly efficient RTP visible to the naked eye under ambient conditions. Lv et al.[187] focused on P1 and P1W, investigating the differences in molecular aggregation structure, electronic transitions, and exciton dynamics of 121 before and after the introduction of water into the P1 system. Calculations showed that the addition of water strengthens intermolecular interactions in P1W by forming a dense and rigid hydrogen bond network, reducing the dihedral angle between the carboxyl group and the benzene ring of 121. This conformational change not only increases the SOC from S1 to Tn, thus accelerating ISC and radiative transition rates and enhancing RTP efficiency, but also reduces the SOC between T1 and S0, inhibiting non-radiative transitions and prolonging RTP lifetime. This study reveals the mechanism by which moisture promotes RTP performance, providing new insights into the development of water-doped materials with RTP properties.
图42 （a）120和121的分子结构；（b）P1和（c）P1W在254 nm照射下UV开启前后的照片（上）和稳态和磷光光谱（下）[186]

Fig. 42 (a).Chemical structures of 120 and 121. (b) P1 and (c) P1W before and after UV is turned on at 254 nm irradiation (top) and steady-state and phosphorescence spectra (bottom)[186]

The stimulus-responsive characteristics of organic RTP materials have been widely used to develop new methods for information storage, sensors, and data encryption[188,189]. Among the organic RTP materials with stimulus-responsive properties, photo-induced RTP materials are a unique class of functional carriers for constructing high-performance sensing and anti-counterfeiting technologies[127,128,149,190]. However, the intrinsic mechanism of irradiation-induced RTP materials is unclear, and molecular design strategies are immature, which limits the development and application of irradiation-induced RTP materials. In 2022, Wang et al.[191] synthesized 122, using a simple fragment to construct an organic RTP crystal with radiation-responsive features (see Figure 43). The crystal exhibited efficient green RTP, showing 14 s of green afterglow in air, with a PLQY of 41.0% for the 122 crystal, where the yields of phosphorescence and fluorescence were 35.2% and 5.8%, respectively. The 122 crystal emitted blue light in air, with a maximum emission wavelength of 387 nm. Notably, 122 exhibited special photo-induced ultralong RTP at 539 nm, with two phosphorescence peaks belonging to the monomer RTP and aggregated RTP of 122. Continuous UV irradiation for about 1 min significantly increased the lifetimes of both monomer and aggregated phosphorescent emitters. The lifetime of the monomer phosphorescence increased from 21.9 µs to 12.4 ms, while the lifetime of the aggregated phosphorescence increased 323.7 times to reach 1392.1 ms. The photo-induced ultralong RTP could spontaneously turn off after being placed in air for 50 min, and this cycle process could be repeated multiple times. The 122 crystal adopted a molecular packing based on multiple intermolecular non-covalent interactions, which was conducive to the formation of RTP. Under UV irradiation, the consumption of oxygen in the crystal matrix led to unique photo-induced RTP. Utilizing the unique photosensitive and oxygen-sensitive properties of the 122 crystal, it has been successfully applied to oxygen sensing and anti-counterfeiting.
图43 （a）122的化学结构和（b）晶体氧检测示意图；（c）不同氧浓度下122晶体图；（d）信息加密到解密的过程示意图[191]

Fig. 43 (a) Chemical structure of 122. (b) Schematic diagram of crystal oxygen detection. (c)122 crystallography at different oxygen concentrations. (d) Schematic diagram of the process from information encryption to decryption [191]

The study of flexible elastic bendable and plastic bendable organic single crystals has become a hotspot in crystal engineering research. Generally, the elasticity and plasticity of crystals are incompatible. Unlike the applications of fluorescent materials, the applications of RTP materials generally ignore the crystallographic properties of large single crystals. Here, Liu et al[192] proposed for the first time an RTP crystal 123 (Figure 44) that combines elasticity and plasticity. The phosphorescence lifetime of the 123 crystal is 279 µs, exhibiting elastic bending (reversible) under external force, and plastic bending (irreversible) after excessive bending. An in-depth study of the irreversible transformation between elastic bending and plastic bending revealed the formation mechanisms of elastically bendable crystals and plastically bendable crystals. Notably, the first phosphorescent light waveguide of a large RTP crystal can not only be achieved in a straight state but also in both elastically bent and plastically bent states. The calculated light loss coefficients for straight crystals, elastically bent crystals, and plastically bent crystals are 0.285, 0.306, and 0.307 dB/mm, respectively.
图44 （a）123的化学结构和123单晶在（b）日光和（c）365 nm紫外光下的照片；（d）单晶123紫外光下在直线形状、弹性弯曲形状和塑性弯曲形状下的磷光波导特性的照片[192]

Fig. 44 (a) Chemical structure of 123 and photographs of 123 single crystals under (b) daylight and (c)365 nm ultraviolet light. (d) Photographs of the phosphorescent waveguide properties of a single crystal 123 under UV light in linear, elastic and plastic bending shapes [192]

7 Multifunctional Organic Luminescent Materials Based on Modified Benzene Rings

In some studies, it is sometimes found that certain luminophores exhibit multiple luminescent properties mentioned earlier and other luminescent mechanisms such as mechanochromism[172]. However, integrating these luminescent mechanisms into a single molecule is usually very difficult and challenging. The development of organic multifunctional luminescent materials with both TADF and AIE characteristics is especially a huge challenge due to severe exciton quenching[193], and small-molecule organic luminescent materials based on benzene that simultaneously possess AIE, TADF, and RTP are even rarer. In the existing reports, most focus on dual luminescence of TADF and RTP. Since the key RISC process and phosphorescent emission for TADF both involve the same Tn state excitons, the balance between RTP and delayed fluorescence can be achieved by adjusting the critical factor ΔEST and its sensitivity to molecular conformation[194]. In previous reports, the molecules are basically of donor-acceptor structures.
To investigate the relationship between multi-channel luminescence and structure of organic light-emitting materials, we[2]used 124as a reference and introduced carbazole or 2-bromocarbazole at the ortho position of the 2,4,6-triphenyl-1,3,5-triazine backbone, obtaining two luminophores 125and 126(Figure 45). All three compounds exhibited high thermal stability, significant solvatochromism, and aggregation-induced quenching. Compared to 125,the introduction of bromine in 126increased its LUMO level, decreased the HOMO level, thereby increasing the energy gap of 126.Under ambient oxygen conditions at room temperature, the PLQYs of solid powders of 124to 126were 7.92%, 32%, and 5.6%, respectively. The solid powders of 125and 126possessed TADF characteristics. 124and 125showed distinct RTP in their crystalline states, with phosphorescence lifetimes of 463.08 and 47.18 ms for 124and 125,respectively. A blue OLED using 125as the guest had turn-on voltage, current efficiency, maximum luminance, and EQE of 4.2 V, 4.2 cd/A, 10389 cd/m2, and 2.64%, respectively.
图45 124~126的化学结构[2]

Fig. 45 Chemical structure of 124~126[2]

As shown in Figure 46, Wen et al. [195] reported on 127 and cultivated two types of crystals, B and Y, with different morphologies. Crystal B exhibited mechanoluminescence and near-UV TADF. At room temperature, the PLQY was 75.2%, with a maximum emission wavelength of 398 nm, and a detected delayed fluorescence lifetime of 842.0 μs. Crystal Y showed dual-peak emissions at 398 and 546 nm; the lifetime detected at 398 nm was the same as that of crystal B, while a long lifetime of 2.1 ms was detected at 546 nm under room temperature, indicating that crystal Y is a multifunctional luminescent material dominated by RTP. The luminescence from TADF and RTP can be reversibly converted under some external stimuli (such as grinding, heating, or smoking), accompanied by a reversible phase transition between the two crystalline phases. The stacking structure of the crystals and the dihedral angle affect the conformation between the molecular T2 and S1, T1 energy levels, leading to the conversion of TADF and RTP luminescence. In addition, effective ISC between Sn and Tn is the reason for the RTP-dominant luminescence in crystal Y. This work provides a new strategy for the molecular design of excitation-responsive luminescent switch materials. He et al. [196] synthesized a donor-acceptor-donor structured 128 composed of benzothiadiazole and thiophene (Figure 47). 128 is highly planar, with a dihedral angle of less than 6° between the donor and acceptor. It fluoresces in solution and powder but induces bright red RTP in the crystal, with a phosphorescence quantum yield of up to 25.0%. After grinding the crystal into an amorphous state, it emits yellow fluorescence, with the lifetime decreasing from 10.9 μs to 3.5 ns, and the emission blue-shifts by 38 nm, demonstrating significant mechanochromism. These results indicate the feasibility of preparing novel crystallization-induced luminescent materials with mechano-blue shift properties.
图46 （a）127的化学结构；（b）B晶和Y晶的发光图像；（c）CIE坐标[195]

Fig. 46 (a) Chemical structure of 127. (b) Luminous images of B and Y crystals. (c) CIE coordinates [195]

图47 128的化学结构，晶体的室温磷光照片（左）和研磨后的荧光照片（右）[196]

Fig. 47 Chemical structure of 128, room temperature phosphorescence photos of crystals (left) and fluorescence photos after grinding (right) [196]

Based on the phthalimide "donor-N-acceptor" (N represents the nitrogen atom of the amide group) structure, Zhang et al.[197]synthesized a class of organic multifunctional luminescent materials 129~131(Figure 48a). The low-temperature fluorescence and phosphorescence spectra of 129~131in crystals estimated ΔE STvalues to be 0.07, 0.06, and 0.05 eV, respectively. A sufficiently small ΔE STpromotes the RISC process, which is conducive to both TADF and RTP. The phosphorescence lifetimes of 129, 130, and 131crystals are 602, 1, and 19 ms, respectively. The strong intramolecular interaction in 129gives it the longest phosphorescence lifetime. The crystals of 129and 130exhibit TADF characteristics with delayed lifetimes of 0.82 and 1.27 ms, respectively. TADF characteristics were observed in the pure films of 129~131at room temperature under aerobic conditions, and the visible afterglow at room temperature can also be effectively used for anti-counterfeiting encryption. Sun et al.[198]synthesized 132with TADF and RTP properties (Figure 49). It exhibits significant TADF characteristics in doped polymethyl methacrylate films, with an estimated ΔE STof 0.19 eV from the low-temperature photoluminescence spectra. The RTP lifetime of the doped film at 477 nm was measured to be 143.79 ms at room temperature. The RTP lifetime of the solid powder at 466 nm excitation was 74 ms at room temperature, with a PLQY of 16.3%. The maximum EQE of the non-doped OLED based on 132is 1.09%, with a turn-on voltage of 3.6 V and a maximum electroluminescence wavelength of 475 nm.
图48 （a）129~131的化学结构；（b）129在365 nm的紫外线照射前后的发光照片[197]

Fig. 48 (a) Chemical structure of 129~131.(b) Luminous photographs of 129 before and after exposure to 365 nm ultraviolet light [197]

图49 （a）132的化学结构；（b）OLED的电致发光光谱，插图为CIE坐标[198]

Fig. 49 (a) Chemical structure of 132. (b) EQE of OLED, illustrated in CIE coordinates [198]

8 Conclusions and Prospects

In summary, benzene has strong chemical modifiability and is widely used in the synthesis of various organic luminescent materials. This paper summarizes from the perspective of chemical modification the recent developments including attaching heteroatoms to the benzene ring, forming an electron transport structure around benzene, constructing a series of color-tunable fluorescent frameworks, regulating CTE by adjusting the length of non-conjugated alkyl chains, or introducing groups on the benzene ring as ligands to achieve phosphorescence of metal complexes. Introducing bridging groups between benzene rings, expanding the conjugation of benzene rings, or through nitrogen atom hybridization within the benzene ring to construct effective electron acceptors, realizing effective separation of HOMO and LUMO in donor-acceptor structures, and promoting RISC to obtain delayed fluorescence materials. On similar construction strategies, it explains how the performance of RTP materials is enhanced by different intermolecular interactions generated by different groups to promote SOC and ISC, and constructing rigid environments to suppress non-radiative transitions and other combined strategies for modifying benzene. Based on this, according to different luminescence mechanisms, the application of modified benzene rings in the synthesis of multifunctional organic luminescent materials such as fluorescent materials, metal-organic complex or cluster phosphorescent materials, TADF materials, AIE materials, and RTP materials are reviewed, and finally, multifunctional organic luminescent materials based on modified benzene with multiple luminescence mechanisms are listed. Overall, small molecule luminescent materials based on benzene are easy to synthesize and have wide applications, being deeply applied in many fields. It is worth noting that multi-resonance TADF materials, relying on conjugation expansion to achieve narrow-band emission, have been a focus in the past two years, but there is no specific research yet on narrowing the emission of RTP materials. Whether the multi-resonance mechanism can narrow the emission of RTP is a question worth pondering. From the perspective of luminescence mechanisms, there is still a lack of integration of multiple luminescence channels at the single-molecule level. The types of multifunctional organic luminescent materials based on modified benzene rings are relatively few, the mechanisms are not well understood, and they are still in their infancy. Moreover, the structures and construction strategies of the reported multifunctional luminescent materials tend to be homogenized, mostly focusing on dual-luminescence mechanisms of TADF and RTP. Therefore, for multifunctional luminescent materials of organically modified small molecules based on benzene, whether it is in-depth exploration based on existing foundations or exploring new application areas, they possess extremely high research value. In today's era of highly developed artificial intelligence, the rational use of computational methods to design the structure of organic luminescent materials, predict excited state properties, and elucidate mechanisms is greatly beneficial to practical experiments and applications. With the deepening of research, it is believed that the future of multifunctional organic luminescent materials based on modified benzene will be even brighter.

References

Publishing order | Descend order by publishing year | Descend order by cited within
[1]
Uoyama H, Goushi K, Shizu K, Nomura H, Adachi C. Nature, 2012, 492(7428): 234.

[2]
Li X, Zheng L F, Tang W, Ye S H, Ma J, Jiang H J. New J. Chem., 2022, 46(33): 16121.

[3]
Rajamalli P, Senthilkumar N, Gandeepan P, Huang P Y, Huang M J, Ren-Wu C Z, Yang C Y, Chiu M J, Chu L K, Lin H W, Cheng C H. J. Am. Chem. Soc., 2016, 138(2): 628.

[4]
Mukherjee S, Thilagar P. Chem. Commun., 2015, 51(55): 10988.

[5]
Carretero A S, Castillo A S, Gutiérrez A F. Crit. Rev. Anal. Chem., 2005, 35(1): 3.

[6]
Galletta M, Puntoriero F, Campagna S, Chiorboli C, Quesada M, Goeb S, Ziessel R. J. Phys. Chem. A, 2006, 110(13): 4348.

[7]
Liao Q Y, Gao Q H, Wang J Q, Gong Y B, Peng Q, Tian Y, Fan Y Y, Guo H J, Ding D, Li Q Q, Li Z. Angew. Chem. Int. Ed., 2020, 59(25): 9946.

[8]
Ekambaram R, Enkvist E, Manoharan G B, Ugandi M, Kasari M, Viht K, Knapp S, Issinger O G, Uri A. Chem. Commun., 2014, 50(31): 4096.

[9]
Xing C, Liu J X, Chen F, Li Y Y, Lv C J, Peng Q C, Hou H W, Li K. Chem. Commun., 2020, 56(30): 4220.

[10]
Yu X, Gao Y C, Li H W, Wu Y. Macromol. Rapid Commun., 2020, 41(14): 2000198.

[11]
Leung N L C, Xie N, Yuan W Z, Liu Y, Wu Q Y, Peng Q, Miao Q, Lam J W Y, Tang B Z. Chem. Eur. J., 2014, 20(47): 15349.

[12]
Hong Y N, Lam J W Y, Tang B Z. Chem. Commun., 2009(29): 4332.

[13]
Watson M D, Fechtenkötter A, Müllen K. Chem. Rev., 2001, 101(5): 1267.

[14]
Ren T B, Xu W, Zhang W, Zhang X X, Wang Z Y, Xiang Z, Yuan L, Zhang X B. J. Am. Chem. Soc., 2018, 140(24): 7716.

[15]
Kim H M, Cho B R. Chem. Rev., 2015, 115(11): 5014.

[16]
Liu X G, Qiao Q L, Tian W M, Liu W J, Chen J, Lang M J, Xu Z C. J. Am. Chem. Soc., 2016, 138(22): 6960.

[17]
Xiang Z, Wang Z Y, Ren T B, Xu W, Liu Y P, Zhang X X, Wu P, Yuan L, Zhang X B. Chem. Commun., 2019, 55(76): 11462.

[18]
Beppu T, Tomiguchi K, Masuhara A, Pu Y J, Katagiri H. Angew. Chem. Int. Ed., 2015, 54(25): 7332.

[19]
Lavis L D, Raines R T. ACS Chem. Biol., 2014, 9(4): 855.

[20]
Liu C, Jiao X J, Wang Q, Huang K, He S, Zhao L C, Zeng X S. Chem. Commun., 2017, 53(77): 10727.

[21]
Kobayashi H, Ogawa M, Alford R, Choyke P L, Urano Y. Chem. Rev., 2010, 110(5): 2620.

[22]
Mandal M, Chatterjee T, Das A, Mandal S, Sen A, Ta M, Mandal P K. J. Phys. Chem. C, 2019, 123(40): 24786.

[23]
Tang B L, Wang C G, Wang Y, Zhang H Y. Angew. Chem. Int. Ed., 2017, 56(41): 12543.

[24]
Kim H, Park W, Kim Y, Filatov M, Choi C H, Lee D. Nat. Commun., 2021, 12(1): 5409.

[25]
Zhang H K, Zhao Z, McGonigal P R, Ye R Q, Liu S J, Lam J W Y, Kwok R T K, Yuan W Z, Xie J P, Rogach A L, Tang B Z. Mater. Today, 2020, 32: 275.

[26]
Zhang H, Tang B Z. J. Am. Chem. Soc. Au., 2021, 1(11): 1805.

[27]
Yamaguchi Y, Matsubara Y, Ochi T, Wakamiya T, Yoshida Z I. J. Am. Chem. Soc., 2008, 130(42): 13867.

[28]
Tu W H, Xiong Z P, Zhang Z T, Zhang J Y, Wang L, Xie Y, Wang Y P, Zhang H K, Sun J Z, Tang B Z. Smart Mol., 2023, 1(2): e20220006.

[29]
Braendle A, Perevedentsev A, Cheetham N J, Stavrinou P N, Schachner J A, Mösch-Zanetti N C, Niederberger M, Caseri W. Chimia, 2017, 71(10): 733.

[30]
Perevedentsev A, Francisco-López A, Shi X Y, Braendle A, Caseri W R, Goñi A R, Campoy-Quiles M. Macromolecules, 2020, 53(17): 7519.

[31]
Wang L, Xiong Z P, Sun J Z, Huang F H, Zhang H K, Tang B Z. Angew. Chem. Int. Ed., 2024, 63(8): e202318245.

[32]
Noda H, Nakanotani H, Adachi C. Sci. Adv., 2018, 4(6): eaao6910.

[33]
Jeon S O, Lee J Y. J. Mater. Chem., 2012, 22(21): 10537.

[34]
Zhang Q W, Fang D, Jiang H J, Zhang X W, Zhang H M. Org. Electron., 2015, 27: 173.

[35]
Su Y J, Huang H L, Li C L, Chien C H, Tao Y T, Chou P T, Datta S, Liu R S. Adv. Mater., 2003, 15(11): 884.

[36]
Song W, Lee J Y. Adv. Opt. Mater., 2017, 5(9): 1600901.

[37]
Di D W, Romanov A S, Yang L, Richter J M, Rivett J P H, Jones S, Thomas T H, Abdi Jalebi M, Friend R H, Linnolahti M, Bochmann M, Credgington D. Science, 2017, 356(6334): 159.

[38]
Lee D, Ma X, Jung J, Jeong E J, Hashemi H, Bregman A, Kieffer J, Kim J. Phys. Chem. Chem. Phys., 2015, 17(29): 19096.

[39]
Chen X F, Xu C, Wang T, Zhou C, Du J J, Wang Z P, Xu H X, Xie T Q, Bi G Q, Jiang J, Zhang X P, Demas J N, Trindle C O, Luo Y, Zhang G Q. Angew. Chem. Int. Ed., 2016, 55(34): 9872.

[40]
Sun X X, Zhang B C, Li X Y, Trindle C O, Zhang G Q. J. Phys. Chem. A, 2016, 120(29): 5791.

[41]
Elbjeirami O, Burress C N, Gabbaï F P, Omary M A. J. Phys. Chem. C, 2007, 111(26): 9522.

[42]
Zhan S Z, Ding F, Liu X W, Zhang G H, Zheng J, Li D. Inorg. Chem., 2019, 58(19): 12516.

[43]
Zheng J, Lu Z, Wu K, Ning G H, Li D. Chem. Rev., 2020, 120(17): 9675.

[44]
Burress C, Elbjeirami O, Omary M A, Gabbaï F P. J. Am. Chem. Soc., 2005, 127(35): 12166.

[45]
Zhang Z Y, Ye D Q, Gao Q Q, Shi Z C, Xie M, Zhan S Z, Huang Y L, Ning G H, Li D. Inorg. Chem. Front., 2021, 8(9): 2299.

[46]
Chen W J, Tian Z M, Li Y G, Jiang Y Q, Liu M H, Duan P F. Chem. Eur. J., 2018, 24(66): 17444.

[47]
Garain S, Sarkar S, Chandra Garain B, Pati S K, George S J. Angew. Chem. Int. Ed., 2022, 61(11): e202115773.

[48]
Huang Z Z, He Z Y, Ding B B, Tian H, Ma X. Nat. Commun., 2022, 13(1): 7841.

[49]
Lin X H, Wang J, Ding B B, Ma X, Tian H. Angew. Chem. Int. Ed., 2021, 60(7): 3459.

[50]
Guang L Y, Lu Y, Zhang Y F, Liao R, Wang F. Angew. Chem. Int. Ed., 2024, 63(8): e202315362.

[51]
Zeng C J, Chen Y X, Kirschbaum K, Lambright K J, Jin R C. Science, 2016, 354(6319): 1580.

[52]
Xie J Z, Yan H B, Sundén B, Xie G N. Appl. Therm. Eng., 2019, 153: 692.

[53]
Zang L, Che Y K, Moore J S. Acc. Chem. Res., 2008, 41(12): 1596.

[54]
Ouyang X, Wang M, Guo L, Cui C, Liu T, Ren Y, Zhao Y, Ge Z, Guo X, Xie G, Li J, Fan C, Wang L. Angew. Chem. Int. Ed., 2020, 59(29): 11836.

[55]
Hossain S, Imai Y, Motohashi Y, Chen Z H, Suzuki D, Suzuki T, Kataoka Y, Hirata M, Ono T, Kurashige W, Kawawaki T, Yamamoto T, Negishi Y. Mater. Horiz., 2020, 7(3): 796.

[56]
Kang X, Zhu M Z. Chem. Soc. Rev., 2019, 48(8): 2422.

[57]
Wu Z N, Liu J L, Gao Y, Liu H W, Li T T, Zou H Y, Wang Z G, Zhang K, Wang Y, Zhang H, Yang B. J. Am. Chem. Soc., 2015, 137(40): 12906.

[58]
Ai L, Jiang W R, Liu Z Y, Liu J L, Gao Y, Zou H Y, Wu Z N, Wang Z G, Liu Y, Zhang H, Yang B. Nanoscale, 2017, 9(34): 12618.

[59]
Kolay S, Maity S, Bain D, Chakraborty S, Patra A. Nanoscale Adv., 2021, 3(19): 5570.

[60]
Yi R H, Liu G Y, Luo Y T, Wang W Y, Tsai H Y, Lin C H, Shen H L, Chang C H, Lu C W. Chem. Eur. J., 2021, 27(51): 12998.

[61]
Sun Y Q, Lei Y L, Liao L S, Hu W P. Angew. Chem. Int. Ed., 2017, 56(35): 10249.

[62]
Goushi K, Yoshida K, Sato K, Adachi C. Nat. Photonics, 2012, 6(4): 253.

[63]
Sun L J, Zhu W G, Wang W, Yang F X, Zhang C C, Wang S F, Zhang X T, Li R J, Dong H L, Hu W P. Angew. Chem. Int. Ed., 2017, 56(27): 7831.

[64]
Liu Y J, Zeng Q X, Zou B, Liu Y, Xu B, Tian W J. Angew. Chem. Int. Ed., 2018, 57(48): 15670.

[65]
Grepioni F, DAgostino S, Braga D, Bertocco A, Catalano L, Ventura B. J. Mater. Chem. C. 2015, 3(36): 9425.

[66]
Lei Y L, Jin Y, Zhou D Y, Gu W, Shi X B, Liao L S, Lee S T. Adv. Mater., 2012, 24(39): 5345.

[67]
Wang Y, Zhu W G, Du W N, Liu X F, Zhang X T, Dong H L, Hu W P. Angew. Chem. Int. Ed., 2018, 57(15): 3963.

[68]
Sun L J, Hua W J, Liu Y, Tian G J, Chen M X, Chen M X, Yang F X, Wang S F, Zhang X T, Luo Y, Hu W P. Angew. Chem. Int. Ed., 2019, 58(33): 11311.

[69]
Zhou H Y, Zhang D W, Li M, Chen C F. Angew. Chem. Int. Ed., 2022, 61(15): e202117872.

[70]
Xue M M, Huang C C, Yuan Y, Zhang Y X, Fung M K, Liao L S. Chem. Commun., 2017, 53(1): 263.

[71]
Albrecht K, Matsuoka K, Fujita K, Yamamoto K. Angew. Chem. Int. Ed., 2015, 54(19): 5677.

[72]
Mei Q B, Weng J N, Tong B H, Tian R Q, Jiang Y Z, Hua Q F, Huang W. Acta Phys. -Chim. Sin., 2014, 30(4): 589.

(梅群波, 翁洁娜, 童碧海, 田汝强, 蒋渊知, 华庆芳, 黄维. 物理化学学报, 2014, 30(3): 332.)

[73]
Yoon J, Kim S K, Kim H J, Choi S, Jung S W, Lee H, Kim J Y, Yoon D W, Han C W, Chae W S, Kwon J H, Cho M J, Choi D H. Chem., 2020, 26(69): 16383.

[74]
Endo A, Sato K, Yoshimura K, Kai T, Kawada A, Miyazaki H, Adachi C. Appl. Phys. Lett., 2011, 98(8):083302.

[75]
Lin T A, Chatterjee T, Tsai W L, Lee W K, Wu M J, Jiao M, Pan K C, Yi C L, Chung C L, Wong K T, Wu C C. Adv. Mater., 2016, 28(32): 6976.

[76]
Hirata S, Sakai Y M, Masui K, Tanaka H, Lee S Y, Nomura H, Nakamura N, Yasumatsu M, Nakanotani H, Zhang Q S, Shizu K, Miyazaki H, Adachi C. Nat. Mater., 2015, 14(3): 330.

[77]
Braveenth R, Lee H, Kim S, Raagulan K, Kim S, Kwon J H, Chai K Y. J. Mater. Chem. C. 2019, 7(25): 7672.

[78]
Achelle S, Hodée M, Massue J, Fihey A, Katan C. Dyes Pigm., 2022, 200: 110157.

[79]
Nakao K, Sasabe H, Komatsu R, Hayasaka Y, Ohsawa T, Kido J. Adv. Opt. Mater., 2017, 5(6): 1600843.

[80]
Salah L, Etherington M K, Shuaib A, Danos A, Nazeer A A, Ghazal B, Prlj A, Turley A T, Mallick A, McGonigal P R, Curchod B F E, Monkman A P, Makhseed S. J. Mater. Chem. C. 2021, 9(1): 189.

[81]
Kato Y, Sasabe H, Hayasaka Y, Watanabe Y, Arai H, Kido J. J. Mater. Chem. C. 2019, 7(11): 3146.

[82]
Krotkus S, Matulaitis T, Diesing S, Copley G, Archer E, Keum C, Cordes D B, Slawin A M Z, Gather M C, Zysman-Colman E, Samuel I D W. Front. Chem., 2021, 8: 572862.

[83]
Aizawa N, Tsou C J, Park I S, Yasuda T. Polym. J., 2017, 49(1): 197.

[84]
Wang F F, Cao X D, Mei L, Zhang X W, Hu J, Tao Y T. Chin. J. Chem., 2018, 36(3): 241.

[85]
Chen J K, Zeng J J, Zhu X Y, Guo J J, Zhao Z J, Tang B Z. CCS Chem., 2021, 3(12): 230.

[86]
Lee J, Aizawa N, Numata M, Adachi C, Yasuda T. Adv. Mater., 2017, 29(4): 1604856.

[87]
Shaikh A M, Sharma B K, Chacko S, Kamble R M. RSC Adv., 2016, 6(65): 60084.

[88]
Pander P, Swist A, Motyka R, Soloducho J, Dias F B, Data P. J. Mater. Chem. C. 2018, 6(20): 5434.

[89]
Siddiqui Q T, Awasthi A A, Bhui P, Muneer M, Chandrakumar K R S, Bose S, Agarwal N. J. Phys. Chem. C, 2019, 123(2): 1003.

[90]
Zhang Q S, Li J, Shizu K, Huang S P, Hirata S, Miyazaki H, Adachi C. J. Am. Chem. Soc., 2012, 134(36): 14706.

[91]
Liu M, Seino Y, Chen D C, Inomata S, Su S J, Sasabe H, Kido J. Chem. Commun., 2015, 51(91): 16353.

[92]
Cummings S D, Eisenberg R. J. Am. Chem. Soc., 1996, 118(8): 1949.

[93]
Ni F, Wu Z B, Zhu Z C, Chen T H, Wu K L, Zhong C, An K B, Wei D Q, Ma D G, Yang C L. J. Mater. Chem. C. 2017, 5(6): 1363.

[94]
Rao J C, Yang L Q, Li X F, Zhao L, Wang S M, Ding J Q, Wang L X. Angew. Chem. Int. Ed., 2020, 59(41): 17903.

[95]
Shao S Y, Hu J, Wang X D, Wang L X, Jing X B, Wang F S. J. Am. Chem. Soc., 2017, 139(49): 17739.

[96]
Yang Y, Zhao L, Wang S M, Ding J Q, Wang L X. Macromolecules, 2018, 51(23): 9933.

[97]
Ren Z J, Nobuyasu R S, Dias F B, Monkman A P, Yan S K, Bryce M R. Macromolecules, 2016, 49(15): 5452.

[98]
Zeng X, Luo J J, Zhou T, Chen T H, Zhou X, Wu K L, Zou Y, Xie G H, Gong S L, Yang C L. Macromolecules, 2018, 51(5): 1598.

[99]
Li C S, Ren Z J, Sun X L, Li H H, Yan S K. Macromolecules, 2019, 52(6): 2296.

[100]
Shao S Y, Wang S M, Xu X S, Yang Y, Lv J H, Ding J Q, Wang L X, Jing X B, Wang F S. Macromolecules, 2019, 52(9): 3394.

[101]
Liu S, Tian Y T, Yan L B, Wang S M, Zhao L, Tian H K, Ding J Q, Wang L X. Macromolecules, 2023, 56(3): 876.

[102]
Wong M Y, Zysman-Colman E. Adv. Mater., 2017, 29(22): 1605444.

[103]
Congrave D G, Drummond B H, Conaghan P J, Francis H, Jones S T E, Grey C P, Greenham N C, Credgington D, Bronstein H. J. Am. Chem. Soc., 2019, 141(46): 18390.

[104]
Kim J H, Yun J H, Lee J Y. Adv. Opt. Mater., 2018, 6(18): 1800255.

[105]
Kim D H, DAléo A, Chen X K, Sandanayaka A D S, Yao D D, Zhao L, Komino T, Zaborova E, Canard G, Tsuchiya Y, Choi E, Wu J W, Fages F, Brédas J L, Ribierre J C, Adachi C. Nat. Photonics, 2018, 12(2): 98.

[106]
Sudyoadsuk T, Chasing P, Kaewpuang T, Manyum T, Chaiwai C, Namuangruk S, Promarak V. J. Mater. Chem. C. 2020, 8(15): 5045.

[107]
Kumsampao J, Chaiwai C, Chasing P, Chawanpunyawat T, Namuangruk S, Sudyoadsuk T, Promarak V. Chem., 2020, 15(19): 3029.

[108]
Madayanad Suresh S, Hall D, Beljonne D, Olivier Y, Zysman-Colman E. Adv. Funct. Mater., 2020, 30(33): 1908677.

[109]
Hatakeyama T, Shiren K, Nakajima K, Nomura S, Nakatsuka S, Kinoshita K, Ni J P, Ono Y, Ikuta T. Adv. Mater., 2016, 28(14): 2777.

[110]
Hu Y X, Miao J S, Hua T, Huang Z Y, Qi Y Y, Zou Y, Qiu Y T, Xia H, Liu H, Cao X S, Yang C L. Nat. Photon., 2022, 16(11): 803.

[111]
Jin J B, Duan C B, Jiang H, Tao P, Xu H, Wong W Y. Angew. Chem. Int. Ed., 2023, 62(18): e202218947.

[112]
Mei J, Leung N L C, Kwok R T K, Lam J W Y, Tang B Z. Chem. Rev., 2015, 115(21): 11718.

[113]
Hu R R, Leung N L C, Tang B Z. Chem. Soc. Rev., 2014, 43(13): 4494.

[114]
Li Q Q, Li Z. Adv. Sci., 2017, 4(7): 1600484.

[115]
Cheng H B, Li Y Y, Tang B Z, Yoon J. Chem. Soc. Rev., 2020, 49(1): 21.

[116]
Yan D Y, Wu Q, Wang D, Tang B Z. Angew. Chem. Int. Ed., 2021, 60(29): 15724.

[117]
Liu B, Tang B Z. Angew. Chem. Int. Ed., 2020, 59(25): 9788.

[118]
Sturala J, Etherington M K, Bismillah A N, Higginbotham H F, Trewby W, Aguilar J A, Bromley E H C, Avestro A J, Monkman A P, McGonigal P R. J. Am. Chem. Soc., 2017, 139(49): 17882.

[119]
Zhang H K, Zheng X Y, Xie N, He Z K, Liu J K, Leung N L C, Niu Y L, Huang X H, Wong K S, Kwok R T K, Sung H H Y, Williams I D, Qin A J, Lam J W Y, Tang B Z. J. Am. Chem. Soc., 2017, 139(45): 16264.

[120]
Zhang J Y, Hu L R, Zhang K H, Liu J K, Li X G, Wang H R, Wang Z Y, Sung H H Y, Williams I D, Zeng Z B, Lam J W Y, Zhang H K, Tang B Z. J. Am. Chem. Soc., 2021, 143(25): 9565.

[121]
Zhang H K, Zhao Z, Turley A T, Wang L, McGonigal P R, Tu Y J, Li Y Y, Wang Z Y, Kwok R T K, Lam J W Y, Tang B Z. Adv. Mater., 2020, 32(36): 2001457.

[122]
Xiong Z P, Zhang J Y, Sun J Z, Zhang H K, Tang B Z. J. Am. Chem. Soc., 2023, 145(38): 21104.

[123]
Gu J, Yue B B, Baryshnikov G V, Li Z Y, Zhang M, Shen S, Ågren H, Zhu L L. Research, 2021, 2021: 9862093.

[124]
Shen S, Baryshnikov G, Yue B B, Wu B, Li X P, Zhang M, Ågren H, Zhu L L. J. Mater. Chem. C. 2021, 9(35): 11707.

[125]
Lee C M, Choi C H, Joo T. Phys. Chem. Chem. Phys., 2020, 22(3): 1115.

[126]
Zhang H K, Du L L, Wang L, Liu J K, Wan Q, Kwok R T K, Lam J W Y, Phillips D L, Tang B Z. J. Phys. Chem. Lett., 2019, 10(22): 7077.

[127]
Gu L, Shi H F, Gu M X, Ling K, Ma H L, Cai S Z, Song L L, Ma C Q, Li H, Xing G C, Hang X C, Li J W, Gao Y R, Yao W, Shuai Z G, An Z F, Liu X G, Huang W. Angew. Chem. Int. Ed., 2018, 57(28): 8425.

[128]
Yang J, Zhen X, Wang B, Gao X M, Ren Z C, Wang J Q, Xie Y J, Li J R, Peng Q, Pu K Y, Li Z. Nat. Commun., 2018, 9: 840.

[129]
Jia X Y, Zhu L L. Acc. Chem. Res., 2023, 56(6): 655.

[130]
Chen T, Chen Z Q, Gong W L, Li C, Zhu M Q. Mater. Chem. Front., 2017, 1(9): 1841.

[131]
Cheng Y, Wang J, Qiu Z, Zheng X, Leung N L C, Lam J W Y, Tang B Z. Adv. Mater., 2017, 29(46): 1703900.

[132]
Sun H, Tang X X, Miao B X, Yang Y, Ni Z H. Sens. Actuat. B Chem., 2018, 267: 448.

[133]
Sun H, Sun S S, Han F F, Zhao Y, Li M D, Miao B X, Nie J, Zhang R, Ni Z H. Chem. Eng. J., 2021, 405: 127000.

[134]
Chen S Y, Pai M H, Liou G S. J. Mater. Chem. C. 2020, 8(22): 7454.

[135]
Ma L L, Liu M X, Liu X Y, Sun W, Lu Z L, Gao Y G, He L. J. Mater. Chem. B. 2020, 8(17): 3869.

[136]
Yin W, Li Y, Li N, Yang W Y, An H, Gao J R, Bi Y, Zhao N. Adv. Opt. Mater., 2020, 8(14): 1902027.

[137]
Wu F Y, Wang L Y, Tang H, Cao D R. Anal. Chem., 2019, 91(8): 5261.

[138]
Du F Y, Li D Q, Ge S, Xie S M, Tang M, Xu Z Q, Wang E J, Wang S M, Tang B Z. Dyes Pigm., 2021, 194: 109640.

[139]
Ruan Z J, Zheng H X, Deng C Y, Cheng X H, Ruan X, Lv S W, Chen Y M, Liu S S, Lin J Q. Dyes Pigm., 2022, 204: 110476.

[140]
Lower S K, El-Sayed M A. Chem. Rev., 1966, 66(2): 199.

[141]
Zhang T, Ma X, Wu H W, Zhu L L, Zhao Y L, Tian H. Angew. Chem. Int. Ed., 2020, 59(28): 11206.

[142]
Zhao W J, He Z K, Lam J W Y, Peng Q, Ma H L, Shuai Z G, Bai G X, Hao J H, Tang B Z. Chem, 2016, 1(4): 592.

[143]
Yang Z Y, Mao Z, Zhang X P, Ou D P, Mu Y X, Zhang Y, Zhao C Y, Liu S W, Chi Z G, Xu J R, Wu Y C, Lu P Y, Lien A L, Bryce M R. Angew. Chem. Int. Ed., 2016, 55(6): 2181.

[144]
Ali Fateminia S M, Mao Z, Xu S D, Yang Z Y, Chi Z G, Liu B. Angew. Chem. Int. Ed., 2017, 56(40): 12160.

[145]
Chai Z F, Wang C, Wang J F, Liu F, Xie Y J, Zhang Y Z, Li J R, Li Q Q, Li Z. Chem. Sci., 2017, 8(12): 8336.

[146]
Hu Y Y, Yao J W, Xu Z, Wang Z F, Li L, Su S J, Ma D G, Huang F. Sci. China Chem., 2020, 63(7): 897.

[147]
Zhang Z Y, Chen Y, Liu Y. Angew. Chem. Int. Ed., 2019, 58(18): 6028.

[148]
Gong Y Y, Chen G, Peng Q, Yuan W Z, Xie Y J, Li S H, Zhang Y M, Tang B Z. Adv. Mater., 2015, 27(40): 6195.

[149]
Ma L W, Sun S Y, Ding B B, Ma X, Tian H. Adv. Funct. Mater., 2021, 31(17): 2010659.

[150]
Wu Z, Nitsch J, Schuster J, Friedrich A, Edkins K, Loebnitz M, Dinkelbach F, Stepanenko V, Würthner F, Marian C M, Ji L, Marder T B. Angew. Chem. Int. Ed., 2020, 59(39): 17137.

[151]
Sasabe H, Kato Y, Watanabe Y, Ohsawa T, Aizawa N, Fujiwara W, Pu Y J, Katagiri H, Kido J. Chem., 2019, 25(71): 16294.

[152]
Chen Y, Xie Y J, Li Z. J. Phys. Chem. Lett., 2022, 13(7): 1652.

[153]
Zhang X P, Xie T Q, Cui M X, Yang L, Sun X X, Jiang J, Zhang G Q. ACS Appl. Mater. Interfaces, 2014, 6(4): 2279.

[154]
Zhang G Q, Chen J B, Payne S J, Kooi S E, Demas J N, Fraser C L. J. Am. Chem. Soc., 2007, 129(29): 8942.

[155]
Chen X, Liu Z F, Jin W J. J. Phys. Chem. A, 2020, 124(14): 2746.

[156]
Głuchowski P, Stręk W, Lastusaari M, Hölsä J. Phys. Chem. Chem. Phys., 2015, 17(26): 17246.

[157]
Zhou B, Yan D P. Adv. Funct. Mater., 2018, 29(4): 1807599.

[158]
Gong Y Y, Zhao L F, Peng Q, Fan D, Yuan W Z, Zhang Y M, Tang B Z. Chem. Sci., 2015, 6(8): 4438.

[159]
Shimizu M, Kimura A, Sakaguchi H. Eur. J. Org. Chem., 2016, 2016(3): 467.

[160]
Liang X, Liu T T, Yan Z P, Zhou Y, Su J, Luo X F, Wu Z G, Wang Y, Zheng Y X, Zuo J L. Angew. Chem. Int. Ed., 2019, 58(48): 17220.

[161]
Zhu H, Liu J K, Wu Y T, Wang L, Zhang H K, Li Q, Wang H, Xing H, Sessler J L, Huang F H. J. Am. Chem. Soc., 2023, 145(20): 11130.

[162]
Xing Y, Wang Y J, Zhou L L, Zhu L L. Dyes Pigm., 2021, 186: 109032.

[163]
Wang X F, Xiao H Y, Chen P Z, Yang Q Z, Chen B, Tung C H, Chen Y Z, Wu L Z. J. Am. Chem. Soc., 2019, 141(12): 5045.

[164]
Lei Y X, Dai W B, Guan J X, Guo S, Ren F, Zhou Y D, Shi J B, Tong B, Cai Z X, Zheng J R, Dong Y P. Angew. Chem. Int. Ed., 2020, 59(37): 16054.

[165]
Ma X K, Zhang W, Liu Z X, Zhang H Y, Zhang B, Liu Y. Adv. Mater., 2021, 33(14): 2007476.

[166]
Kuila S, Ghorai A, Samanta P K, Siram R B K, Pati S K, Narayan K S, George S J. Chem., 2019, 25(70): 16007.

[167]
Jeon I R, Jeannin O, Clérac R, Rouzières M, Fourmigué M. Chem. Commun., 2017, 53(36): 4989.

[168]
Triguero S, Llusar R, Polo V, Fourmigué M. Cryst. Growth Des., 2008, 8(7): 2241.

[169]
Shen Q J, Pang X, Zhao X R, Gao H Y, Sun H L, Jin W J. CrystEngComm, 2012, 14(15): 5027.

[170]
Wang H, Hu R X, Pang X, Gao H Y, Jin W J. CrystEngComm, 2014, 16(34): 7942.

[171]
Liu Z F, Chen X, Wu W X, Zhang G Q, Li X, Li Z Z, Jin W J. Spectrochim. Acta Part A Mol. Biomol. Spectrosc., 2020, 224: 117428.

[172]
Ishi-i T, Tanaka H, Kichise R, Davin C, Matsuda T, Aizawa N, Park I S, Yasuda T, Matsumoto T. Chem., 2021, 16(15): 2136.

[173]
Ishi-i T, Kichise R, Park I S, Yasuda T, Matsumoto T. J. Mater. Chem. C. 2023, 11(8): 3003.

[174]
Garain S, Singh A K, Peter S C, George S J. Mater. Res. Bull., 2021, 142: 111420.

[175]
Wu Y N, Gui H Q, Ma L W, Zou L, Ma X. Dyes Pigm., 2022, 198: 110005.

[176]
Nidhankar A D, Goudappagouda, Mohana Kumari D S, Chaubey S K, Nayak R, Gonnade R G, Pavan Kumar G V, Krishnan R, Babu S S. Angew. Chem. Int. Ed., 2020, 59(31): 13079.

[177]
Chen B, Huang W H, Su H, Miao H, Zhang X P, Zhang G Q. Angew. Chem. Int. Ed., 2020, 59(25): 10023.

[178]
Xiong Y, Zhao Z, Zhao W J, Ma H L, Peng Q, He Z K, Zhang X P, Chen Y C, He X W, Lam J W Y, Tang B Z. Angew. Chem. Int. Ed., 2018, 57(27): 7997.

[179]
Su Y, Zhang Y F, Wang Z H, Gao W C, Jia P, Zhang D, Yang C L, Li Y B, Zhao Y L. Angew. Chem. Int. Ed., 2020, 59(25): 9967.

[180]
Wu H W, Chi W J, Chen Z, Liu G F, Gu L, Bindra A K, Yang G B, Liu X G, Zhao Y l. Adv. Funct. Mater., 2018, 29(10): 1807243.

[181]
Thomas H, Pastoetter D L, Gmelch M, Achenbach T, Schlögl A, Louis M, Feng X L, Reineke S. Adv. Mater., 2020, 32(19): 2000880.

[182]
Shu H Y, Li H, Rao J C, Chen L, Wang X, Wu X F, Tian H K, Tong H, Wang L X. J. Mater. Chem. C. 2020, 8(41): 14360.

[183]
Deng Y, Li P, Li J, Sun D, Li H. ACS Appl. Mater. Interfaces, 2021, 13(12): 14407.

[184]
Gutierrez G D, Sazama G T, Wu T, Baldo M A, Swager T M. J. Org. Chem., 2016, 81(11): 4789.

[185]
Garain S, Garain B C, Eswaramoorthy M, Pati S K, George S J. Angew. Chem. Int. Ed., 2021, 60(36): 19720.

[186]
Xu S, Wang W, Li H, Zhang J Y, Chen R F, Wang S, Zheng C, Xing G C, Song C Y, Huang W. Nat. Commun., 2020, 11: 4802.

[187]
Lv A Q, Gong W Q, Lv K Q, Ma Q, An Z F, Ma H L. Adv. Optical Mater., 2024, 12(7): 2301937.

[188]
Huang L L, Qian C, Ma Z Y. Chem., 2020, 26(52): 11914.

[189]
Wang T, Hu Z B, Nie X C, Huang L K, Hui M, Sun X, Zhang G Q. Nat. Commun., 2021, 12(1): 1364.

[190]
Wang C, Yu Y, Yuan Y H, Ren C Y, Liao Q Y, Wang J Q, Chai Z F, Li Q Q, Li Z. Matter, 2020, 2(1): 181.

[191]
Xie N, Wang J X, Huang T T, Zhao L P, Sun P, Lu G Y, Wang Y, Li C L. Adv. Optical Mater., 2022, 10(17): 2200767.

[192]
Liu H, Bian Z Y, Cheng Q Y, Lan L F, Wang Y, Zhang H Y. Chem. Sci., 2019, 10(1): 227.

[193]
Yang G, Ran Y, Wu Y M, Chen M Q, Bin Z Y, You J S. Aggregate, 2022, 3(2): e127.

[194]
Wang Y S, Yang J, Tian Y, Fang M M, Liao Q Y, Wang L W, Hu W P, Tang B Z, Li Z. Chem. Sci., 2020, 11(3): 833.

[195]
Wen Y T, Xiao S B, Liu H C, Tian X Z, De J B, Lu T, Yang Z Q, Zou D Y, Lv Y, Zhang S T, Su Q, Yang B. J. Mater. Chem. C. 2021, 9(48): 17511.

[196]
He G, Du L L, Gong Y Y, Liu Y L, Yu C B, Wei C, Yuan W Z. ACS Omega, 2019, 4(1): 344.

[197]
Zhang L, Li M, Hu T P, Wang Y F, Shen Y F, Yi Y P, Lu H Y, Gao Q Y, Chen C F. Chem. Commun., 2019, 55(81): 12172.

[198]
Sun J, Jia J, Zhao B, Yang J, Singh M, An Z, Wang H, Xu B, Huang W. Chin. Chem. Lett., 2021, 32(4): 1367.

Options
Outlines

/

〈 〉