Modulating NeH-based excited-state intramolecular proton transfer by different electron-donating/withdrawing substituents in 2-(2′-aminophenyl) benzothiazole compounds

The NeH-based excited-state intramolecular proton transfer process of 2-(2'-aminophenyl) benzothiazole (PBT-NH2) and its three derivatives have been explored by the time-dependent density functional theory (TD-DFT) method. The scanned potential energy curves reveal that the energy barriers of the first singlet excited state of the four compounds along the ESIPT reactions are predicted at 8.74, 8.98, 6.72 and 1.69 kcal/mol respectively, suggesting that the inclusion of a strong electron-withdrawing tosyl (Ts) group can remarkably facilitate the occurrence of the ESIPT reaction, while the involvement of an electron-donating methyl group has slight opposite effect on the ESIPT process of the amino-type hydrogen-bonding system.