R–D–A and R–D−π–A Structured AIEgens: Relationship between Electronic, Conformational Characteristics and Photophysical Properties

The design of new aggregation-induced emission luminogens (AIEgens) has aroused continuous attention. The relationship between structure and performance plays an important role in guiding such efforts. In this contribution, two R–D–A- and R–D−π–A-type AIEgens were facilely designed and synthesized, that is, DPE-PTZ-CN and DPE-PTZ-PCN, with diphenylethylene as the twisted rotor structure (R), phenothiazine as electron-donor (D), and the (aryl) cyano group as electron-acceptor (A) fragments. Both luminophores were endowed with typical AIE properties, while their α AIE (PL intensity ratio of AIEgen in a mixed solution with water fraction ( f w ) = 90 vol % to that with f w = 0) were quite different. The α AIE for DPE-PTZ-CN was as high as 41, but it was only 3 for DPE-PTZ-PCN, in which the π-bridge (aryl linker) was introduced between its D and A groups. In addition, the push–pull electronic effect endowed both molecules with the feature of intramolecular charge transfer (ICT). The solvatochromism effect observed in solutions with different polarities confirmed the existence of the ICT process. The theoretical calculation and single crystal structure analysis revealed that the electronic structure and molecular conformation characteristics had a decisive influence on the differences in photophysical behaviors.