How the atomic electron-accepting ability affect the double ESIPT process of 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol?

Abstract

By adopting the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, the effects of atomic electron-accepting ability on the double excited state intramolecular proton transfer (ESIPT) processes of the molecules (BBO, BBT and BBSe) were systematically investigated. The obtained bond lengths, bond angles and IR vibration analysis prove that the strength of the hydrogen bonds in the three molecules gradually increases from BBO to BBT and BBSe. Moreover, the potential energy surfaces and topology analysis indicate that all the three molecules prefer to the ultrafast stepwise double ESIPT reaction in the S1 state. And the excited state proton transfer occurs more easily in the studied molecular systems along with the weakened electron-accepting ability of atom. It is concluded that the decreasing electron-accepting ability of atom can promote the molecular ESIPT behavior, which provides the theoretical basis for the synthesis of the new molecular systems with double ESIPT properties.