Solvent effects on the ESIPT mechanism of 3-(benzo[d]thiazol-2-yl)triphenylen-2-ol: a DFT investigation

Abstract

The excited-state intramolecular proton transfer (ESIPT) mechanism of 3-(benzo[d]thiazol-2-yl)triphenylene-2-ol (HTpT) in different kinds of solvents was calculated, utilizing density functional theory (DFT) and time-dependent density functional theory (TD-DFT). We investigated the effects of five solvents, namely methanol (MeOH), dichloromethane (DCM), tetrahydrofuran (THF), chloroform (CHCl₃), and toluene, on the system. Analysis of hydrogen bonding parameters and infrared vibrational spectra in a series of solvents showed the hydrogen bond strengthens with decreasing solvent polarity in the S₁ state, a finding supported by our analysis of the interaction region indicator (IRI) function. The energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) was reduced, as the polarity of the solvent decreases. In addition, the potential energy curves (PECs) in the S₀ and S₁ states calculated for all solvents indicated that the ESIPT process becomes less feasible with increasing solvent polarity, whereas it becomes more favorable with decreasing solvent polarity. Notably, our study identifies toluene as the most effective solvent among the five studied in promoting the ESIPT process.