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

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 excitedstates, and concluded that proton transfer processes in probe 1 and 2 are apt to happen in the S-1 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. (C) 2020 Elsevier B.V. All rights reserved.