Liu Rui, Ran Huijuan, Zhao Zhen, Yang Xueli, Zhang Jiali, Chen Lijuan, Sun Huaming, Hu Jian-Yong
Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Key Laboratory for Advanced Energy Devices, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xian 710119, China.
National Demonstration Center for Experimental Chemistry Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xian 710119, China.
ACS Omega. 2018 May 31;3(5):5866-5875. doi: 10.1021/acsomega.8b00583.
In dipolar organic π-conjugated molecules, variable photophysical properties can be realized through efficient excited-state intramolecular charge transfer (ICT), which essentially depends on the π-conjugation patterns. Herein, we report a controllable regioselective strategy for synthesis and optical properties of two donor-acceptor (DA)-type 1,3,5,9-tetraarylpyrenes (i.e., 1,3-A/5,9-D () and 1,3-D/5,9-A ()) by covalently integrating two phenyl rings and two -OMe/CHO-substituted phenyl units into the 2--butylpyrene building block, in which the two phenyl rings substituted at the 1,3-positions act as acceptors for or as donors for and the two -OMe or -CHO-substituted phenyl moieties substituted at the K-region of 5,9-positions act as donors for or as acceptors for , respectively. Density functional theory calculations on their frontier molecular orbitals and UV-vis absorption of S → S transition theoretically predicted that the change of π-conjugation directions in the two DA pyrenes could be realized through a variety of substitution patterns, implying that the dissimilar ground-state and excited-state electronic structures exist in each molecule. Their single-crystal X-ray analysis reveal their highly twisted conformations that are beneficial for inhibiting the π-aggregations, which are strikingly different from the normal 1,3,5,9-tetraphenylpyrenes () and related 1,3,6,8-tetraarylpyrenes. Indeed, experimental investigations on their optical properties demonstrated that the excited-state ICT pathways can be successfully controlled by the change of π-conjugation directions through the variety of substitution positions, resulting in the modulations of emission color from deep-blue to green in solution. Moreover, for the present DA pyrenes, highly fluorescent emissions with moderate-to-high quantum yields both in the thin film and in the doped poly(methyl methacrylate) film were obtained, suggesting them as promising emitting materials for the fabrication of organic light-emitting diodes.
在偶极有机π共轭分子中，可通过高效的激发态分子内电荷转移（ICT）实现可变的光物理性质，这主要取决于π共轭模式。在此，我们报道了一种可控的区域选择性策略，用于合成两种供体-受体（DA）型1,3,5,9-四芳基芘（即1,3-A/5,9-D（）和1,3-D/5,9-A（））及其光学性质，方法是将两个苯环和两个-OMe/CHO取代的苯基单元共价整合到2-丁基芘结构单元中，其中在1,3位取代的两个苯环分别作为的受体或的供体，而在5,9位的K区域取代的两个-OMe或-CHO取代的苯基部分分别作为的供体或的受体。对其前沿分子轨道和S→S跃迁的紫外可见吸收进行密度泛函理论计算，从理论上预测了通过各种取代模式可实现两种DA芘中π共轭方向的改变，这意味着每个分子中存在不同的基态和激发态电子结构。它们的单晶X射线分析揭示了其高度扭曲的构象，这有利于抑制π聚集，这与普通的1,3,5,9-四苯基芘（）和相关的1,3,6,8-四芳基芘显著不同。实际上，对其光学性质的实验研究表明，通过改变π共轭方向和各种取代位置，可以成功控制激发态ICT途径，从而在溶液中实现发射颜色从深蓝色到绿色的调制。此外，对于目前的DA芘，在薄膜和掺杂聚甲基丙烯酸甲酯薄膜中均获得了具有中等到高量子产率的高荧光发射，这表明它们是用于制造有机发光二极管的有前途的发光材料。
