Coumarin 102 excitation in aqueous media: contributions of vibronic coupling and hydration

Abstract

For the first time, vibronic coupling was considered when analyzing the excitation of coumarin C102. It was found that the M05 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 C102 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 N7 (“A” type) and the CO carbonyl group of the dye (“B” type).