Theoretical study on the excited-state intramolecular proton-transfer reaction of 10-hydroxybenzo[h]quinoline in methanol and cyclohexane

The dynamics of the excited-state intramolecular proton-transfer (ESIPT) reaction of 10-hydroxybenzo-quinoline (HBQ) in different solvents, have been investigated based on the time-dependent density functional theory (TD-DFT) in detail. Upon excitation, the intramolecular hydrogen bond between the hydroxyl and phenanthrene functionality is significantly strengthened in the S-1 state, which can be used as a reasonable tendency for facilitating the ESIPT process. In addition, the calculated vertical excitation energies in the So state and S-1 state reproduce the experimental UV-vis absorbance and fluorescence emission spectra well. Through calculating the fluorescence spectra of the HBQ chromophore, two outcomes for this chromophore were found in the S-1 state, which demonstrates that the ESIPT process occurs. The potential energy curves have been calculated to account for the mechanism of the proton-transfer process in the excited-state. As a result, the barrierless ESIPT process can occur in the S-1 state with proton transfer from the O atom to the N atom. And maybe the ESIPT process is easier in methanol solvent due to the higher potential energy difference. (C) 2014 Elsevier B.V. All rights reserved.