Abstract

Solute-solvent interactions in liquids govern the ultrafast optical dynamics of vibronic excitations and play a key role in chemical reactions. Most of the experimental techniques applied so far on optical dephasing and solvation dynamics give no detailed information on local solute-solvent geometries and - thus - provide only limited insight into the microscopic mechanisms [1]. Here we demonstrate for the first time that vibrational spectroscopy can serve as a sensitive local probe. In particular, we show that the carbonyl functional group of coumarin dyes is affected by hydrogen-bonding with the solvent and analyze how this hydrogen bonding affects the optical dynamics. In the femtosecond measurements, coumarin 102 (C102) is excited to the S₁ state by a 100 fs pulse in the visible and the resulting change of the vibrational spectra is probed by 100 fs pulses tunable in the mid-infrared between 1500 and 1750 cm¹.

© 1998 IEEE