Coumarin 314 excitation in aqueous media: Contributions of vibronic coupling and hydration

Abstract

Vibronic coupling and hydrogen bonding were considered when analyzing the excitation of coumarin C314. It was found that the B3PW91 functional in combination with the 6–31++G(d,p) basis set and the IEFPCM solvent model gives a calculated vibronic absorption spectrum, which is in good agreement with the experimental one both in the position of the maximum and in shape. Significant differences are shown between the results of calculating the transition energies using the models of vertical and vibronic transitions. Both a single C314 molecule and its five different hydration complexes with strongly bound water molecules have been analyzed. It was taken into account that a water molecule can attach both to the nitrogen atom N1 (“A” type) and the C=O carbonyl groups of the dye (“B” type). The vibronic emission spectra of a single C314 molecule and its hydrate complexes were also calculated and analyzed.