一个有趣的发现，分子结构简单的非共轭桥联的Salen配体虽然只拥有很小的Π共轭体系，但是却能通过聚集诱导荧光增强，实现红、黄、绿、兰荧光。非共轭桥联可以对荧光强度和波长进行调控。

Functionalized Salen ligands linking with non-conjugated bridges: unique and colorful aggregation-induced emission, mechanism, and applications

Jinghui Cheng, Yuanxi Li, Rui Sun, Jiaoyan Liu, Fei Gou, Xiangge Zhou, HaifengXiang,* and Jin Liu*

J. Mater. Chem. C, 2015, 3, 11099-11110.

A series of novel, simple, and colorful Salen ligands (56 samples), salicylaldehyde-based bis-Schiff bases, linking with differentnon-conjugated alkyl bridges ((CH₂)_n, n = 2-9, 12; cyclohexyl) and containing different electron-accepting (-NO₂, -F, and-Cl), electron-donating (-OMe, -OH, and -NEt₂), or steric hindrance (-t-butyl) substituents or p-extended system (naphthalene ring) have been designed and synthesized. The photophysical properties of these Salen ligands can be well-tuned by the introduction of side functional substituents, p-extended system, and central N-alkyl chain bridges. It is unusual that they contain a small p-conjugated system but display strong blue, green,and red aggregation-induced emission (AIE) with large Stokes shifts (up to 162 nm) and high fluorescencequantum yields (up to 0.44 and 0.75 in water and solid, respectively). Combining with their advantages of AIE and good stability and biocompatibility, the Salen ligands can be potentially used in mechanofluorochromism (crystal-defect-inducedemission) and living cell imaging. Moreover, the inherent relationships between their chemical structures and AIE properties are studied, which provide unequivocal insights for the design of AIE-active dyes.