Vibrational relaxation from electronically photoexcited states in solution studied by the acoustic peak delay method: hydrogen bonding effect to betaine-30

The rate of the temperature rise, which represents the vibrational relaxation rates of many vibrational levels in the excited and the ground states, is studied in various solvents by using the peak delay method of the transient acoustic grating after the S3→S0 internal conversion of betaine-30. It is found that a small amount of water efficiently relaxes the vibrational energy. The rate shows a clear correlation with the number of the hydroxy group of the solvent per unit volume. We interpreted this correlation as evidence that the energy of the solute transferred to solvent efficiently through the hydrogen bonding.