新型高效深红/近红外有机荧光材料的设计制备及其器件研究

Thanks to their wide applications in white OLEDs with high color rendering index, information-secured display, optical communication,medical therapy, deep-red and near infrared (NIR) organic materials and organic light-emitting diodes (OLEDs) have aroused growing attention. To note, conventional deep-red/NIR OLEDs virtually give very low external quantum efficiencies (EQEs) due to the low photoluminescence quantum efficiency (PLQY). Herein, this project aims to improve the efficiency of deep-red/NIR OLEDs by using novel materials and mechanisms, respectively. As for novel materials, on the one hand, we plan to synthesize a series of high efficiency non-donor-acceptor (non-D-A) type deep-red/NIR fluorescent materials with aggregation-induced emission (AIE) based on thiadiazole and selenadiazole derivatives. For the other hand, two strategies, i.e. the use of ring-closed structure and the introduction of methyl groups at the ortho-position are incorporated to increase the rigidity of molecules and thus improve the PLQY of materials. And with the aid of quantum chemical calculations, we plan to reveal the rational design strategies of high efficiency deep-red/NIR fluorescent materials. As for novel mechanism, for one thing based on our group previous proposed mechanism of thermally activated delayed fluorescence (TADF) sensitized fluorescence in visible region, we plan to synthesize stable green to orange emission TADF materials and using them as sensitized hosts for high efficiency deep-red/NIR emitters. For another, we plan to use triplet fusion featured materials as hosts to sensitize high efficiency deep-red/NIR fluorescent emitters. Incorporating novel materials and mechanisms, we aim to realize high efficiency deep-red/NIR OLEDs with low efficiency roll-off, which could satisfied the requirement for high quality flat-displays, high color rendition index (CRI) solid-state lighting and information-secured displays, etc.

为了实现显色指数优异的白光OLED及信息安全、光学通讯等领域急需的显示和照明，高效深红/近红外(DR/NIR)有机发光材料和器件亟待发展。但受能隙规则所限，随着发光波长的红移，传统有机发光材料的发光效率显著降低。本项目拟从新材料和新机理两方面入手，设计制备高效DR/NIR有机发光材料和器件。在新材料方面，一方面基于萘并噻/硒二唑系列的非D-A型分子结构，拟引入具有聚集诱导发光特性的AIE基团，设计合成具有AIE特性的高效DR/NIR固态荧光材料；另一方面，在传统D-A型结构基础上，通过引入刚性闭环结构或者邻位位阻效应抑制分子的非辐射跃迁，实现高效DR/NIR热活化延迟荧光材料。借助量化计算探讨高效DR/NIR有机发光材料的理性设计策略。在新机理方面，拟遴选具有高效热活化延迟荧光或高效三线态融合特性的材料作为主体，有效利用三线态激子，提高DR/NIR-OLED的量子效率、降低效率滚降。

深红/近红外有机发光材料和器件在信息安全、夜视、生物成像、光医疗、光学通讯等方面有着广阔的应用前景和迫切需求。但受限于能隙规则，实现高效深红/近红外发光是非常具有挑战性的科学难题。该项目通过四年的研究，在新型高效深红/近红外有机荧光材料的设计、制备及器件研究等方面取得了一系列创新性研究成果。圆满完成了原定计划的研究内容，达到了预期的研究目标。主要成果有：1）基于萘并硒二唑基团，构建了一类HOMO-LUMO高度重叠的非典型给体-受体结构近红外有机荧光材料，采用主客体分离策略与主体热活化敏化近红外发光机制，将荧光OLED的激子利用率从25%提高到58%，实现了高效率、低效率滚降的有机近红外荧光器件。2）基于强给体-受体结构，构建了一类新型的分子间电荷转移聚集体（CTA）近红外有机发光材料。CTA的形成不仅可有效降低材料的单三线态能差，诱导并增强热活化延迟荧光（TADF），还能抑制激发态的非辐射跃迁，呈现突破能隙规则限制的新现象，从而在固态下实现了近100%的PLQY。3）基于这类CTA实现了一系列高效的深红/近红外OLEDs，发光峰值在675nm、710nm、730nm和752nm处的最大EQE达到24.8%、17.0%、13%和6.8%，并且首次实现了近红外II区TADF发光，为近红外II区TADF材料的设计与发展奠定了基础。4）重新回顾了能隙规则的基础理论，提出降低电子非绝热耦合项是抑制非辐射跃迁的另一有效策略。实验和理论研究表明，CTA的形成一方面可以减小激发态的电子和空穴重叠来降低电子非绝热耦合，从而抑制非辐射跃迁获得高效NIR光致发光，另一方面则可以大幅稳定激发态能量，诱导TADF的产生并实现高效NIR电致发光。该工作对分子聚集体的光物理行为和基础理论研究进行了有益探索，同时为减轻能隙规则的限制实现高效有机近红外发光材料的设计开发提供了新策略。已发表标注的SCI论文共6篇，包括Adv.Mater.，Adv.Funct.Mater.，Sci.China:Chem.，Chem.Commun.等。其中2019年发表Adv.Mater.论文入选ESI高被引论文。新申请中国发明专利6项，国内外会议邀请报告5人次。培养毕业博士1名，并于2018年入选国家博士后创新人才支持计划；毕业硕士1名，出站博士后2名。