Switching of emissive and NLO properties in push–pull chromophores with crescent PPV-like structures
作者:Carmine Coluccini、Arvind K. Sharma、Marco Caricato、Angelo Sironi、Elena Cariati、Stefania Righetto、Elisa Tordin、Chiara Botta、Alessandra Forni、Dario Pasini
DOI:10.1039/c2cp43140h
日期:——
We report on a series of novel homologous pushâpull compounds, in which identical donor (a dimethylamino) and acceptor (a malonate ester) functionalities endcap crescent PPV fragments, bearing, respectively, 1, 2 and 3 p-phenylenevinylene units in direct linear conjugation (compounds 7â9). The three compounds exhibit striking differences in their linear and nonlinear optical properties. The shorter compound 7 exhibits aggregation-induced emission with a strong luminescence in the solid state (blue emission, photoluminescence quantum yield 38%), and it is nonemissive in solution; the more extended conjugated systems 8 and 9 show classical aggregation-caused quenching in the solid state, while high quantum yield photoluminescence (21 and 93% in toluene) is restored in diluted solutions, through mechanisms involving intramolecular charge transfer in the excited states. EFISH measurements in solutions demonstrate a strong solvent and concentration dependence. As rationalized with the aid of molecular modelling, compounds 8 and, more markedly, 9 aggregate in stable centrosymmetric dimers in solution.
我们报告了一系列新型同源推拉化合物,其中相同的供体(二甲基氨基)和受体(丙二酸酯)官能团在新月形 PPV 片段的末端,分别带有 1、2 和 3 个对苯乙烯单元,直接线性共轭(化合物 7-9)。这三种化合物在线性和非线性光学特性方面表现出惊人的差异。较短的化合物 7 在固态下表现出聚集诱导发射的强发光(蓝色发射,光致发光量子产率为 38%),并且在溶液中无辐射;较长的共轭体系 8 和 9 在固态下表现出经典的聚集诱导淬灭,而在稀释溶液中通过激发态分子内电荷转移机制恢复了高量子产率光致发光(在甲苯中分别为 21% 和 93%)。溶液中的 EFISH 测量结果表明,它与溶剂和浓度有很大关系。借助分子建模,化合物 8 和更明显的化合物 9 在溶液中聚集成稳定的中心对称二聚体。