摘要/Abstract

热活化延迟荧光分子因具有高效发光、价格低廉等优点，在发展有机发光二极管方面显示出巨大潜力.与单分子相比，激基复合物容易实现小的单线态-三线态能隙差，在开发延迟荧光材料方面备受关注.然而，相应受体材料的种类仍较为稀少，且激基复合物延迟荧光性质与受体材料结构之间的关系还需深入探讨.本工作设计合成出两个新型的基于螺芴氧杂蒽的电子受体材料（CNSFDBX和DCNSFDBX）.结果表明，它们与给体材料TCTA掺杂后均呈现激基复合物发射，其中TCTA：DCNSFDBX掺杂体系显示更高的发光效率，其原因归结为双氰基取代使得DCNSFDBX具有更强的接收电子的能力.该工作为开发新型电子受体材料用于激基复合物延迟荧光提供了思路.
关键词: 螺芴氧杂蒽, 激基复合物发光, 热活化延迟荧光, 空间位阻, 氰基取代
Thermally activated delayed fluorescence (TADF) molecules have great potential in developing organic light-emitting diodes (OLEDs) because of their efficient emission and low price. Compared to pure-molecules, exciplex systems are drawing much attention since they can realize small singlet-triplet energy splitting (ΔE_ST) more easily for TADF. However, the species and molecular design systems of electron-acceptors for exciplex-TADF are still limited even though some acceptors have been reported. In addition, the relationship between TADF properties and the structures of acceptors requires further investigations. Herein, we report the design and synthesis of two novel spiro[fluorine-9,9'-xanthene]-based acceptors (CNSFDBX and DCNSFDBX) for achieving exciplex-emissions by using tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as a donor. The photoluminescence measurements suggest that both of the doping-systems (TCTA:CNSFDBX and TCTA:DCNSFDBX) possess exciplex emissions. Whereas, it is observed that the TCTA:DCNSFDBX system displays higher photoluminescence quantum yield and electroluminescence efficiency than TCTA:CNSFDBX. For better explaining this phenomenon, we perform low-temperature fluorescence and phosphorescence spectra investigations. The experimental results show that the TCTA:DCNSFDBX system exhibits smaller ΔE_ST values (0.12 eV) than TCTA:CNSFDBX (0.46 eV). This results indicate that the reverse intersystem crossing from non-radiative triplet states (T₁) to radiative singlet states (S₁) and TADF processes can be realized more easily in the TCTA:DCNSFDBX system. Moreover, the electrochemical measurements and theoretical calculations suggest that the lowest unoccupied molecular orbital (LUMO) level of DCNSFDBX (-2.86 eV) is lower than that of CNSFDBX (-2.47 eV). This situation implies that DCNSFDBX possesses stronger electron-accepting ability than CNSFDBX with the help of dicyano-substitution. Furthermore, the TCTA:DCNSFDBX system displays larger driving force (0.39 eV) than TCTA:CNSFDBX (0.22 eV) in their exciplex-formation processes, suggesting the exciplex-emission (TCTA:DCNSFDBX) can be achieved more easily. Therefore, the higher exciplex-emission efficiencies of the TCTA:DCNSFDBX system are attributed to the stronger electron-acceptability of DCNSFDBX through dicyano- substitution and larger driving force in its exciplex emission process. This work provides a route to further development of new electron-acceptors for exciplex-TADF.
Key words: spiro[fluorine-9,9'-xanthene], exciplex emission, thermally activated delayed fluorescence, steric hindrance, cyano-substitution


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