Opposite ESIPT characteristic of two AIE-active isomers with different linkage sites

In this work, we report two isomers composed of 1-phenyl-1H-phenanthro[9,10-d]imidazole (PI), hydroxyl and tetraphenylethylene (WE), abbreviated as m-PITPE and p-PITPE. It is found that they exhibit similar aggregation-induced emission (AlE) behavior but totally different excited-state intramolecular proton transfer (ESIPT) characteristic, as a result of the different linkage sites of PI on TPE moiety. Theoretical calculations and their different experimental responses to F- demonstrate that only the paralinkage isomer displays ESIPT. In m-PITPE with meta-linkage, the electron cloud distribution only locates at the WE part in the singlet excited (Si) states, which results in the localized excited state without ESIPT characteristic. (C) 2019 Elsevier Ltd. All rights reserved.