Time-resolved fluorescence and hole-burning line shapes of solvated molecules: Longitudinal dielectric relaxation and vibrational dynamics

Abstract

We develop a microscopic theory of time- and frequency-resolved fluorescence and hole-burning measurements of polar, polyatomic molecules in a polar solvent. The line shapes are expressed in terms of gas phase spectroscopic parameters of the solute, vibrational relaxation rates, laser pulse shapes, and the dynamics of a solvation coordinate. These dynamics are then related to the frequency and wave vector dependent dielectric function of the solvent. Both fluorescence and hole-burning line shapes are predicted to show significant line narrowing at short times, and to undergo broadening and a red shift as the solvent relaxes. We propose hole burning as an alternative to fluorescence measurements in probing solvation dynamics. The time scale of the solvent induced line shift and line broadening is found to be independent of the shape of the solute, in contrast with previous work. The effects of vibrational relaxation are distinguished from those of solvent relaxation.