How is the AIE mechanism profoundly changed in an ESIPT family: the novel introduction of a tetraphenylethene group onto (Z)-3-(quinolin-2-ylmethylene)-3,4-dihydroquinoxalin-2(1H)-one.

It is reported that two derivatives of (Z)-3-(quinolin-2-ylmethylene)-3,4-dihydroquinoxalin-2-(1H)-one (1) with a tetraphenylethene (TPE) group introduced at amide N atom of the dihydroquinoxalinone moiety (2) or at phenyl ring of the quinoline fragment (3) are synthesized, and the derivatives exhibit a remarkably enhanced aggregation-induced emission (AIE) activity than the parent. Although both the parent and the derivatives have the characteristic of an excited state intramolecular proton transfer (ESIPT), the AIE mechanism of 2 and 3 is totally different from that of 1. The considerably stronger emission of 3 than that of 2 should be attributed to the unique crystallization-induced emission enhancement (CIEE) effect.