Tactfully regulating the ESIPT and TICT mechanism in the AIE-active multifunctional triphenylamine Schiff-base compound (TPASB) by methyl substitution.

The triphenylamine Schiff-base (TPASB) with dual proton transfer sites (N…H-O [R1] and N…H-O [R2]), which is crucial in the field of optoelectronic materials. Herein, a novel molecular design strategy for preparing of TPASB-1 and TPASB-2 via the selective methylation of the hydroxyl group at the R2 or R1 position was proposed. The analysis of electronic structures and potential energy surfaces revealed that a single excited state intramolecular proton transfer (ESIPT) process of TPASB occurs only at R1. Nevertheless, the ESIPT process of TPASB-2 was successfully turned on at R2. More noteworthy is that compared to TPASB, the methylation of hydroxyl group at the R2 position triggers the TICT process of TPASB-1, effectively reducing the potential barrier of ESIPT at the R1 position. This theoretical study explains the role of the substituent effect in regulating ESIPT behaviour, and provides valuable guidance for synthesising efficacious ESIPT-active compounds.