Organic light-emitting diodes are a revolutionary technology in the contemporary fields of display and lighting, and their working mechanism based on current-driven organic material luminescence marks unique self-luminescent characteristics, which stand in sharp contrast to traditional display technologies that rely on external backlight sources^［10］. The basic structure of OLED is shown in Fig. 1 (a), typically consisting of a substrate, transparent conductive anode, hole transport layer (HTL), emitting layer (EML), electron transport layer (ETL), and metal cathode. In addition, to further enhance performance, OLED structures usually incorporate a hole injection layer (HIL), electron injection layer (EIL), hole blocking layer (HBL), and electron blocking layer (EBL)^［17-25］. Transparent conductive glass substrates generally use indium tin oxides (ITO) as the anode material for bottom-emission OLED structures. Typical top electrodes of bottom-emission OLEDs commonly use highly conductive metals such as silver and aluminum, which also possess high reflectivity.

The typical OLED luminescence process is shown in Fig. 1(b), mainly including the following four steps: (1) Carrier injection: under the action of an externally applied driving voltage, electrons and holes from the cathode and anode will move towards the organic luminescent layer of the device; (2) Carrier transport: electrons and holes respectively pass through the corresponding transport layers to reach the organic luminescent layer, where they accumulate in large quantities at the interface of this layer; (3) Carrier recombination: when a certain number of holes and electrons accumulate at the interface of the organic luminescent layer, they will recombine to form excitons; (4) Exciton luminescence: excitons produced by recombination at the interface of the luminescent layer will activate the organic luminescent material, causing its outermost electrons to transition from the ground state to the excited state. Due to the instability of the high - energy excited state, the electrons will return to the ground state and release energy in the form of light, thus completing the entire device's luminescence process^［26］.

The core of OLED display technology lies in the luminescent materials, which determine the final performance of the device, including color saturation, brightness, and lifespan. If high-quality OLED displays and solid-state lighting are to be achieved, it is essential to develop energy-saving and long-lasting luminescent materials that can be widely used. Based on the trichromatic theory, the effective combination of red, green, and blue light is the key to achieving full-color gamut display^［27］. Although red and green OLED materials have been widely used in commercial products, the development of highly efficient and long-lasting blue light OLED materials remains a significant challenge in the field.

According to the classification based on the luminescence mechanism and the development of OLED luminescent materials, blue OLED materials can be divided into three categories: first-generation traditional fluorescent materials, second-generation phosphorescent materials, and third-generation thermally activated delayed fluorescence (TADF) materials^［28］. The luminescence mechanisms of the three generations of materials are shown in Figure 3. In the process of organic electroluminescence, both singlet and triplet excitons are generated simultaneously, with 25% being singlet excitons and 75% being triplet excitons. Excitons at high energy states are usually unstable and lose energy through different pathways to return to the ground state. These pathways include radiative transitions and non-radiative transitions. Radiative transitions refer to light emission through fluorescence or phosphorescence processes, while non-radiative transitions include vibrational relaxation, internal conversion, external conversion, and intersystem crossing (ISC)^［29］. Singlet excitons emit fluorescence through radiative transitions to the ground state, and triplet excitons emit phosphorescence through radiative transitions to the ground state. Due to the forbidden effect of radiative transitions, triplet excitons mainly undergo non-radiative decay, contributing little to luminescence and relying only on singlet excitons for radiative transition light emission^［30］. Therefore, for traditional organic fluorescent materials, the internal quantum efficiency (IQE) is at most 25%^［31］. By utilizing heavy metal complexes to excite 75% triplet excitons, the second generation of OLED luminescent materials (i.e., phosphorescent materials) was developed. People utilize the enhanced spin-orbit coupling effect induced by heavy metal atoms, resulting in heavy metal complexes that can accelerate radiation deactivation from the lowest triplet state T₁ to the ground state S₀ through phosphorescent emission, promoting ISC from the lowest singlet state S₁ to T₁^［32］. This strategy and relaxation pathway using triplets can achieve an internal quantum efficiency of 100% for phosphorescent heavy metal emitters. Thermally activated delayed fluorescence occurs because of the small energy gap between the lowest singlet state and the lowest triplet state. When the lifetime of T₁ excitons is long enough, the normally spin-forbidden reverse intersystem crossing (RISC) process is thermally activated, allowing triplet excitons to up-convert to the S₁ state, from which they radiatively transition to the ground state, achieving fluorescence emission involving triplet excitons^［33］. For TADF materials, theoretically, IQE can also reach 100%, which is key to obtaining high external quantum efficiency (EQE) OLED devices^［34］.

In the field of OLED technology, by precisely controlling the material composition and energy level structure of the red, green, and blue emission layers, it is possible to achieve a continuous spectrum covering the visible light spectrum range from a single device. This spectral synthesis effect enables OLED devices to exhibit highly efficient and high-quality white light illumination. Among these three primary colors, red and green luminescent materials have reached a highly mature level of industrial production due to long-term research and technological innovation, demonstrating excellent performance stability and color purity. However, although blue OLED materials have made significant progress in recent years, their performance optimization and lifespan improvement still lag behind those of red and green materials. This is mainly due to the technical challenges faced by blue materials in terms of charge injection efficiency, energy conversion efficiency, and long-term operational stability. Therefore, breakthroughs in blue light technology are particularly crucial for achieving high-efficiency, energy-saving white light and the development of the entire lighting industry. The chromaticity range of blue light materials can be subdivided into four main categories through CIE_y values: ultra-deep blue (CIE_y < 0.05), deep blue (CIE_y < 0.010), blue (CIE_y < 0.25), and sky blue (CIE_y < 0.35)^[35]. Developing deep blue emitters is a fundamental requirement for achieving high-quality displays and solid-state lighting. Additionally, promising deep blue emitters must also comply with the National Television System Committee (NTSC) standards and the International Commission on Illumination (CIE) coordinates (0.14, 0.08) to meet the requirements of full-color display applications^[36].

The classic building blocks of traditional blue fluorescent materials mainly include anthracene, pyrene, fluorene, carbazole, phenanthroimidazole, etc. Most blue fluorescent materials are derivatives of anthracene. For example, MADN and TMADN (structures as shown in Figure 3) and other commercialized blue light materials are designed and synthesized based on anthracene^[37]. Anthracene-derived blue light materials not only have good stability but also high fluorescence quantum yield. This is because they possess a wide bandgap, rigid chemical structure, and excellent charge transport properties. Additionally, anthracene-based materials exhibit good thermal stability and film-forming properties, which are beneficial for OLED fabrication. However, due to the planar structure of anthracene, it is prone to aggregation-induced crystallization issues, thus typically requiring chemical modification to avoid this problem. To prevent fluorescence quenching and aggregation-induced crystallization, bulky substituents are usually introduced at the 9 and 10 positions of anthracene, adjusting the emission from blue to deep blue and enhancing its thermal stability^[38].

Blue phosphorescent materials are typically complexes of iridium or platinum^［39-40］. Blue phosphorescent materials can be traced back to 2001, when Forrest et al. first used Firpic to prepare a blue phosphorescent OLED (CIE = 0.16, 0.29) with an EQE of 5.7% and an emission wavelength of 475 nm^［41］. Firpic (as shown in Figure 3) is also the most reported blue phosphorescent complex. When preparing phosphorescent devices, because the energy gap of blue light materials is relatively large, selecting suitable wide-energy-gap blue light host materials presents a considerable challenge. Extensive research has shown that the most important factor in improving the efficiency of blue phosphorescent devices is choosing the appropriate host material. In recent years, researchers have successfully developed numerous blue phosphorescent materials, which not only aim to further enhance the optoelectronic performance of OLED devices but also focus on extending their service life and improving color purity. The progress in this research direction provides new momentum and possibilities for the future development of OLED technology.

The earliest research on blue TADF materials began in 2012, pioneered by Adachi et al. The DTC-DPS (Fig. 3) they synthesized exhibited excellent device performance, marking the starting point of TADF research^[42]. In the early studies of blue TADF materials, the properties of TADF molecules were finely tuned by designing donor-acceptor structures and adjusting different combinations of donors and acceptors. The key was to ensure effective separation between the donor and acceptor, thereby achieving effective separation of the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), thus reducing the energy gap (ΔE_ST) between the lowest singlet excited state (S₁) and the lowest triplet excited state (T₁)^[42], which is crucial for accelerating the reverse intersystem crossing (RISC) process. Recently, the introduction of B-N resonance structures has brought new directions to TADF research, known as Multi-Resonance Thermally Activated Delayed Fluorescence (MR-TADF)^[43]. MR-TADF materials utilize the resonance effect produced by electron-deficient boron groups/carbonyl groups and electron-rich oxygen/nitrogen atoms, minimizing the bonding/antibonding of frontier molecular orbitals to reduce vibrational relaxation in polycyclic structures, thereby achieving a narrow Full Width at Half Maximum (FWHM) and high luminescence efficiency^[44-45].

Although blue phosphorescent and TADF materials can theoretically achieve 100% internal quantum efficiency (IQE) and OLED devices with higher external quantum efficiency have been fabricated, they still face many challenges in practical applications. For instance, phosphorescent materials are costly and pose environmental pollution problems due to the necessity of using heavy metal atoms, while TADF materials, although reducing costs and improving EQE, still have issues with color purity and lifespan that need to be addressed, and the phenomenon of efficiency roll-off is relatively severe. Currently, traditional fluorescent materials based on anthracene derivatives still dominate among commercial blue materials, demonstrating the importance of stability and cost-effectiveness in commercial applications.

The molecule of bianthracene is composed of two anthracene units connected by a single carbon-carbon bond, and its molecular structure is diverse with a total of five isomers: 1,1'-bianthracene, 2,2'-bianthracene, 1,9'-bianthracene, 2,9'-bianthracene, and 9,9'-bianthracene (the molecular structures are shown in Figure 4). The structural characteristics of each isomer influence their photoelectric properties such as light absorption, luminescence efficiency, and stability, which also determine their application potential in OLED devices to varying degrees. As a key core material for OLEDs, the low-cost synthesis of organic materials is a complex and diversified field that encompasses various chemical methods and processes. During the synthesis process, optimizing reaction conditions and catalysts to reduce by-product formation and improve the quality and production efficiency of the target product is crucial for cost reduction. The synthetic route for bianthracene-based blue light materials is relatively simple, especially since many isomeric bianthracene monomers can be synthesized in a simple one-step reaction. In 2019, Li Zhanfeng's team reported a series of 9,9'-bianthracene derivatives with high-efficiency blue-light-emitting hosts and deep-blue luminescent materials synthesized at low cost. By simplifying the synthesis process without affecting the luminescence performance of the materials, the manufacturing cost of blue-light-emitting materials was minimized to the greatest extent^［48］. In fact, the synthesis process of 9,9'-bianthracene derivatives is generally simple. This characteristic not only ensures the safety and controllability of industrial-scale production but also greatly promotes the low-cost and highly efficient preparation of large quantities of blue-light-emitting materials on a gram scale or even larger, driving the low-cost development and application of OLED panels.

Among numerous anthracene isomers, 9,9'-bianthracene materials have significantly improved the luminescence efficiency and service life of OLED devices due to their outstanding high fluorescence quantum efficiency and excellent thermal stability. Their unique wide bandgap structure ensures high color purity blue light emission, meeting the stringent requirements of international standards. Meanwhile, their characteristics of low turn-on voltage, high current efficiency, and high energy efficiency effectively reduce the power consumption of the device and enhance the overall device efficiency. Moreover, the bipolar transport properties of 9,9'-bianthracene materials simplify the device structure design, making them highly favored and extensively explored in the research and application of OLED blue-emitting materials. The following will delve into the application progress of 9,9'-bianthracene and its derivatives in the OLED field and comprehensively summarize their device performance.

Beyond the exploration of 9,9'-bianthryl and its applications in organic light-emitting diodes, the bianthryl family also encompasses other structurally diverse isomers such as 1,1'-bianthryl, 2,2'-bianthryl, 1,9'-bianthryl, and 2,9'-bianthryl (molecular structures shown in Figure 8). These different structural variants not only broaden the research horizon of bianthryl materials but also provide new avenues for application development in the optoelectronic field. Although derivatives of 1,1'-bianthryl, such as DMBA (47)^[71] and (48)^[72], have not yet been applied in the optoelectronic field, 2,2'-bianthryl-derived TPBA (49) is often used as a green-light emitting host material or hole transport layer material in OLEDs and organic field-effect transistors^{[49, 73-77]}. Meanwhile, although the derivative development of 1,9'-bianthryl and 2,9'-bianthryl is still in its early stages, they have already demonstrated potential application value in specific fields such as photon upconversion luminescence (TTA)^[78-79].

With the development of ultra-high-definition 4K and 8K resolution displays, their unprecedented fine image quality and immersive visual impact are driving the rapid innovation of display light sources. In this context, the BT.2020 standard has emerged as a color benchmark for ultra-high-definition video content, complementing 4K/8K technology and jointly defining the standards for a new generation of visual feasts^［80］. At the same time, the BT.2020 standard broadens the color performance capabilities of these OLED display devices, enabling them to present a wider, more accurate, and vivid color range, providing users with a near real-world visual experience.

Compared with the NTSC standard, the BT.2020 standard allows a 1.5-fold increase in color gamut, covering approximately 75.8% of the CIE 1931 color space chromaticity diagram. Such a large expansion of the color gamut is due to the redefinition of the RGB primary colors' CIE coordinates: red light as (0.708, 0.292), green light as (0.170, 0.797), and blue light as (0.131, 0.046)^［81］. To achieve this leading standard, the development of high color purity blue OLED emitting materials is the core critical issue. Traditional luminescent materials require extremely deep blue emission to meet the BT.2020 blue light standard because their wide spectrum can easily cover adjacent green regions, thereby significantly affecting the CIE_y value. Currently, reported luminescent materials with color coordinates close to the BT.2020 blue light standard mainly rely on dynamic combinations of electron-donating/electron-accepting pairs, such as Cz-derived donor units modulating acceptor units or acridine-derived donor units paired with weak acceptor units. Among 9,9'-bianthryl materials, only a few exhibit electroluminescence close to the BT.2020 standard blue light, such as BA (component 1) with an emission peak wavelength of 432 nm and a color coordinate CIE_y of 0.05^［48］, and MBAn-(3,4,5)-F (component 35) with an emission peak wavelength of 440 nm and a color coordinate CIE_y reaching 0.053^［68］. Therefore, future design of 9,9'-bianthryl blue luminescent materials may achieve appropriate blue shifts while maintaining electroluminescent conversion efficiency by introducing strong electron acceptor units, modulating intramolecular charge transfer, and increasing molecular rigidity, thereby aligning their CIE coordinates with the BT.2020 blue standard.

In the in-depth exploration of the optoelectronic properties of bianthracene materials, the structural differences between isomers are particularly crucial to their performance. We applied density functional theory (DFT) using the Gaussian 09 software with the B3LYP/6-31G(d) basis set to model and analyze the ground state (S₀) structures and frontier molecular orbital energy levels of five different molecular structures of bianthracene (as shown in Figure 4). Through theoretical calculations, we discovered significant effects of bianthracene isomerization in three main aspects. First, different molecular structures result in different spatial configurations, directly affecting the packing modes and interactions between molecules. For example, as can be seen from Figure 4, the dihedral angles between anthracene units in 1,1'-bianthracene, 2,2'-bianthracene, 1,9'-bianthracene, 2,9'-bianthracene, and 9,9'-bianthracene exhibit clear differences, being 76.7°, 90.3°, 38.2°, 75.8°, and 90.0° respectively. These structural twists not only enhance the thermal stability of the material but also promote fluorescence quantum yield by increasing molecular rigidity and reducing the possibility of non-radiative transitions. In particular, the reduction in intermolecular interactions in orthogonal structures helps mitigate fluorescence quenching caused by molecular aggregation, thereby further enhancing luminescence efficiency. Second, variations in molecular structure also affect electronic structure, influencing electron injection and transport properties in devices. For instance, 1,9'-bianthracene exhibits HOMO and LUMO distributions on different anthracene units, unlike other structures centered on bianthracene, suggesting that 1,9'-bianthracene may have stronger intramolecular charge transfer, potentially causing a redshift in the spectrum, which is detrimental to luminescent performance. Finally, different molecular structures lead to variations in photophysical properties. In 2021, Zhao et al. found that 9,9'-bianthracene with an orthogonal geometry showed more pronounced solvent polarity dependence, longer fluorescence lifetimes, and higher spin-orbit charge transfer efficiency compared to the more coplanar 2,9'-bianthracene^[78]. In 2023, Kang et al.'s research further explored the differences in symmetry-breaking charge transfer (SB-CT) between 9,9'-bianthracene and TPBA due to different anthracene unit connection methods, revealing significant short-range CT coupling differences between geometrically planarized TPBA and 9,9'-bianthracene^[82]. Through these comprehensive analyses, we not only deepen our understanding of the effects of bianthracene isomerization on material optoelectronic properties but also provide important scientific guidance for the future design and development of high-performance blue OLED materials.

The substitution of halogen has a significant impact on the performance of bianthracene-based blue light organic electroluminescent diode materials. Research has found that derivatives introducing halogen atoms onto the bianthracene molecular skeleton exhibit superior electroluminescent performance in OLED devices. This enhancement in performance is mainly attributed to the unique electrochemical properties of halogen atoms, including their high electronegativity, which enables them to effectively attract electron clouds within the molecule, thereby lowering the molecular energy levels. Additionally, halogen substitution can significantly reduce the injection barriers for electrons and holes, promoting efficient transmission of electrons and holes, thus enhancing the luminescence efficiency of OLED devices. The introduction of halogen atoms not only affects electronic properties but also significantly improves the overall stability of the material. The carbon-halogen bonds formed between halogen and carbon atoms possess high polarity and bond energy, greatly enhancing the chemical stability of halogen-substituted bianthracene derivatives under light or current excitation. Moreover, the presence of halogen atoms reduces π-π stacking between molecules, diminishing fluorescence quenching caused by molecular aggregation, thereby further optimizing luminescent performance. Halogen substitution not only alters the electronic structure and optical properties of molecules but also plays an important role in their spatial arrangement and intermolecular interactions. For instance, halogen substitution can improve intermolecular interactions and packing modes by influencing the three-dimensional configuration of molecules, which is crucial for controlling exciton formation and transport in OLED devices. Furthermore, halogen substitution can optimize the photophysical properties of molecules, such as adjusting emission wavelengths and increasing quantum yields, providing new strategies for designing and developing high-performance blue light OLED materials. In summary, the halogen substitution effect plays a key role in enhancing the performance of bianthracene-based blue light OLED materials. By finely tuning the position and quantity of halogen substitutions, the electronic structure and optoelectronic properties of materials can be further optimized, paving new pathways for developing highly efficient and stable OLED luminescent materials.

In the technology of organic light-emitting diodes, the asymmetric effect of bianthracene molecules plays a crucial role. This effect is mainly reflected in two aspects: first, the asymmetrically substituted 9,9'-bianthracene molecules affect the properties of their excited states, including local excited states and charge transfer states, by altering their electronic structure. Such structural changes can not only cause shifts in absorption and emission spectra but also alter fluorescence quantum yield. Additionally, the typical symmetry-breaking charge transfer characteristics of 9,9'-bianthracene enable directional charge separation under low driving force, providing a new approach for optimizing the performance of OLED materials. By applying asymmetric substitution to 9,9'-bianthracene, researchers are able to modulate the carrier migration rate, thereby optimizing the overall performance of OLED devices. This asymmetric substitution strategy not only helps achieve higher luminescence efficiency and a broader range of emission spectrum modulation but also effectively enhances the thermal stability and operational lifetime of the materials.

With the deepening understanding of the influence mechanism of asymmetric effects, researchers have begun to explore the use of this effect to design and synthesize novel bianthracene derivatives. For instance, by introducing various functional side chains at different positions of 9,9'-bianthracene, the electronic properties and spatial configuration of the molecules can be further adjusted, thereby achieving precise control over OLED performance. These studies not only broaden our understanding of the application of asymmetric effects in optoelectronic materials but also provide important design principles and synthetic strategies for developing next-generation high-efficiency blue-light OLED materials.

Appropriate steric hindrance can not only prevent over-dense packing between molecules, thereby reducing exciton quenching, but also significantly improve charge transport efficiency. By introducing bulky side chains or functional groups, intermolecular π-π interactions can be effectively reduced, thus decreasing aggregation-induced fluorescence quenching and improving the thermal stability of the material.

Recent studies have shown that steric hindrance not only improves the electronic and photophysical properties of molecules but also directly affects the photoelectric conversion efficiency and lifetime of OLED devices by regulating molecular packing modes and charge transport characteristics. In particular, designing molecules with steric hindrance can promote more efficient charge injection and balance charge transport, thereby improving the operational lifetime of the device. For example, deep blue OLEDs based on TBBA anthracene derivative 30 have a half-life of only 42 minutes at an initial brightness of 500 cd·m^-2 when the device is placed in an inert gas glove box^［48］. However, the deep blue OLED device using the DITBDAP emitter, developed through effective steric hindrance effects, has been reported by researchers to achieve a T₉₅ lifetime of up to 250 hours under high brightness conditions of 3000 cd·m^-2. In fact, compared to red and green OLED devices, blue OLED devices generally exhibit shorter operational lifetimes. Therefore, adopting an effective steric hindrance strategy enables the development of high-performance 9,9'-bianthracene derivative blue light materials that combine efficiency and stability^［83］.

Moreover, specific spatial steric configurations can lead to large Stokes shifts and multiple emission phenomena, providing new possibilities for achieving wide color gamut and high color purity in OLED display technology. Additionally, the spatial steric effect also helps to break the conversion barrier between triplet and singlet states, improving exciton utilization. This is particularly important for enhancing the luminescence efficiency of OLEDs, as the formation and utilization of triplet excitons is one of the key strategies for improving luminescence efficiency in many OLED materials.

By intricately designing and synthesizing bianthracene-based luminescent materials with effective steric hindrance, the performance of OLED devices can be significantly enhanced, including improvements in luminous efficiency, thermal stability, and extended device lifespan. However, compared to red and green luminescent materials, wide-bandgap 9,9'-bianthracene blue luminescent materials exhibit lower exciton utilization and are prone to efficiency roll-off at high current densities. Particularly for blue phosphorescent and TADF luminescent materials, high emission energy (>2.7 eV) and long triplet exciton lifetimes can easily lead to hot exciton or hot polaron losses through exciton annihilation processes, thereby accelerating material and OLED device aging. An effective approach is to disperse 9,9'-bianthracene blue luminescent materials in a high-energy host to reduce exciton concentration and mitigate exciton annihilation. Typically, the host exciton energy in the emissive layer of OLED devices does not generate photons directly through the host but is transferred to 9,9'-bianthracene blue dopant guests via Förster and Dexter energy transfer mechanisms. Ultimately, the dopant radiatively emits light with the assistance of the host suppressing intermolecular interactions and non-radiative quenching. Based on this, by optimizing factors such as the thickness, energy level matching, and doping concentration of adjacent transport layer materials, it ensures that carriers can be efficiently balanced and transported across functional layers and recombine to emit light efficiently, thereby enhancing the electroluminescent blue light performance of the device. Currently, the performance of wide-bandgap host materials such as exciplex hosts, mixed hosts, and bipolar hosts surpasses that of unipolar hosts and single TADF hosts^［84］. Among mixed hosts, exciplexes outperform traditional mixed hosts in terms of device lifetime. In singlet hosts, bipolar and TADF hosts exhibit better device longevity than unipolar hosts. Therefore, different device structures need to be designed based on the performance of various hosts to maximize the regulation of 9,9'-bianthracene blue OLED performance.

This paper delves into the application of 9,9'-bianthracene-based blue light-emitting materials in organic light-emitting diodes (OLEDs), providing a detailed analysis of their molecular structure, performance relationship, and impact on the performance of OLED devices. By systematically reviewing research progress on symmetric structures, asymmetric structures, and alkyl-substituted 9,9'-bianthracene-based blue light-emitting materials, it highlights the importance of these materials in improving the performance of blue light OLED devices. In addition to conventional bianthracene derivatives, this review also extends to other members of the bianthracene family, such as 1,1'-bianthracene and 2,2'-bianthracene, which, although still in the exploratory stage for OLED applications, have already shown potential in the optoelectronic field. The research on these materials not only broadens the application scope of bianthracene-based materials but also provides new ideas and directions for future optoelectronic device design and development. Finally, special emphasis is placed on the important role of bianthracene isomerization effects, fluorine substitution effects, asymmetric effects, and steric hindrance effects in modulating the luminescence performance of blue light OLED materials. These molecular design strategies are not only significant for understanding the fundamental science of blue light OLED materials but also have practical application value for designing and developing novel high-efficiency blue light-emitting materials.

To further develop high-performance bianthracene-based blue light OLED materials and devices, the future research work on 9,9'-bianthracene will mainly progress from the following aspects: