Revelation solvent effects: excited state hydrogen bond and proton transfer of 2-(benzo[d]thiazol-2-yl)-3-methoxynaphthalen-1-ol

Abstract

2-(Benzo[d]thiazol-2-yl)-3-methoxynaphthalen-1-ol (MMT) is one of the key materials for making naphthalene. Distinguishing photophysical phenomena of MMT were observed in different solvents [U. Warde and S. Nagaiyan, J. Photochem. Photobiol., A, 2017, 337, 33]. However, the solvent effect on the hydrogen bond dynamical process has not been carefully analyzed theoretically. Based on state-of-the-art ab initio calculations, we provide a molecular-level investigation where excited-state hydrogen bonds and proton transfers are affected by solvent polarity. The computed absorption and fluorescence emission spectra of MMT are in agreement with the experimental peak values. The calculated hydrogen bond parameters and infrared vibration spectra confirm the excited-state hydrogen bond enhancing mechanism and uncovered the intensity of the excited-state hydrogen bond weakening as a perfect solvent polarity augment. Importantly, Hirshfeld charges unveiled that the excited-state hydrogen bond strength depends on solvent effects and electronegativity of the proton donor and proton acceptor. Based on frontier molecular orbitals of MMT, we found that the degree of charge transfer gradually increased with an increase in solvent polarity. By analyzing the potential energy curves, we concluded that the excited state intramolecular proton transfer (ESIPT) reaction of MMT is gradually inhibited by increasing solvent polarity. Revealing the mechanism of solvent effects will help to develop new products in optoelectronics and analytical tools.