The theoretical study about the ESIPT mechanism for 2,4‐bis(benzooxazol‐2′‐yl)hydroquinone: Single or double?

Abstract

AbstractOn the basis of the density functional theory (DFT) and time‐dependent DFT (TDDFT) methods, we theoretically study the excited‐state intramolecular proton transfer (ESIPT) mechanism of 2,4‐bis(benzooxazol‐2′‐yl)hydroquinone (2,4‐DHBO), which is reported in the previous literature (Ulrich et al. New J. Chem. 2016, 40, 5877). The calculated absorption and fluorescence spectra of 2,4‐DHBO are accordant with previous experiment, which indicates that the selective theoretical method is credible. The comparisons of the calculated bond lengths, angles, infrared, and Raman vibrational spectra of 2,4‐DHBO manifest that two intramolecular hydrogen bonds (HBs) strengthen in the excited state (S1), which should be triggered the ESIPT reaction. In addition, the calculated frontier molecular orbitals (MOs) and the map of the electron density difference between the ground (S0) and S1 states provide that the ESIPT reactions are facilitated by charge transfer after photoexcitation. Moreover, to explore the detailed ESIPT mechanism of 2,4‐DHBO, the potential energy surfaces (PESs) in the S0 and S1 states are constructed. Because of the low excited‐state potential barriers on the PESs of 2,4‐DHBO, the single and stepwise double ESIPT mechanisms are revealed in the S1 state, which is different from single ESIPT mechanism proposed by experiment. We hope the detailed ESIPT mechanism of this fluorophore based on my theoretical research will help researchers to design such kinds of fluorophores in the future.