摘要/Abstract
近年来, 作为第三代有机发光二极管(organic light-emitting diodes, OLED)发光材料的热活化延迟荧光(thermally activated delayed fluorescence, TADF)材料受到了学术界和产业界的广泛关注. TADF分子由于其单线态与三线态之间的能级差较小, 三线态激子可以被环境热活化而通过反系间窜越上转换至单线态, 理论上可实现100%的激子利用率, 从而使得OLED器件外量子效率显著提高. TADF材料被认为是突破高效稳定有机电致蓝光发射瓶颈的潜在解决方案. 一般, TADF分子为含有电子给体(donor, D)和电子受体(acceptor, A)的纯有机推拉电子体系. 通过改变给体单元和受体单元的结构、数量和取代基及其位置可以有效调节TADF分子的单线态-三线态能级差、前线轨道分布、聚集态结构、电致发光颜色及其性能. 同时取代基在调控给、受体单元的推拉电子能力及TADF材料的分子构型、聚集态结构和稳定性等物化特性方面扮演着非常重要的角色. 本综述分别对D-A型和多重共振型TADF蓝光分子的取代基效应进行了综述, 以期为高效稳定的蓝光TADF分子的设计合成提供有效借鉴.
关键词: 蓝光发光体, 热活化延迟荧光, 小分子, 取代基, 有机发光二极管
As the third-generation emitters for organic light-emitting diodes (OLED), thermally activated delayed fluorescence (TADF) materials have attracted widespread attention from both academic and industrial communities in recent years. In TADF molecules, the triplet excitons can be upconverted to the singlet state with the aid of ambient thermal energy by virtue of the reverse intersystem crossing (RISC) owing to the small singlet-triplet splitting energy (ΔEST). Therefore, 100% exciton utilization efficiency can be theoretically realized by harvesting both singlet and triplet excitons. Consequently, the external quantum efficiencies of OLEDs can be significantly improved compared with the first-generation devices based on conventional fluorophores. TADF materials are regarded as an effective potential solution to break through the bottleneck of highly efficient and stable blue organic electroluminescence (EL). Generally, TADF molecules is a purely organic push and pull system containing at least an electronic donor and acceptor. The Δ EST, frontier orbital distributions, aggregation structures, EL colors and device performance can be effectively tuning by changing the structures and quantities of the donor and the acceptor, the substituents and their substituted positions. Meanwhile, the substituents of TADF molecules play a crucial role in the regulation of the strengths of donor and acceptor, molecular configurations, aggregation structures, stabilities and other physical and chemical properties. The substituent effects of purely organic blue TADF molecules from D-A type and multiple-resonance type blue TADF molecules are summarized, in the hope of providing effective reference for the design and synthesis of high-efficiency and stable blue light TADF molecules.
Key words: blue emitter, thermally activated delayed fluorescence, small molecule, substituent, OLED
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