Theoretical investigation on the ESIPT mechanism and fluorescent sensing mechanism of 2-(2′-hydroxyphenyl) thiazole-4-carboxaldeyde in methanol

Abstract

2-(2'-Hydroxyphenyl) thiazole-4-carboxaldeyde (aldehyde 1) and hemiacetal 2 were selected to study the mechanism of excited-state intramolecular proton transfer and the detecting of Al3+ ion in methanol by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. Our theoretical results are in good agreement with the experimental values. The intramolecular H-bond is enhanced in the first excited-state based on the analyses of structural parameters, frontier molecular orbitals and electronic spectra. The stronger intramolecular H-bond is more favorable for ESIPT process. In order to further demonstrate the proton transfer process, we constructed the potential energy curves of probe 1 and 2 in both ground- and excited-states, and concluded that proton transfer processes in probe 1 and 2 are apt to happen in the S1 state. In addition, the Mayer bond order, energy gap and absorption and fluorescence spectra were applied to interpret the process of detection of Al3+ ion.