Resonance Raman Studies of Solvent Dynamics in Solvatochromic Systems

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McHale is supported by the Experimental Physical Chemistry Program for studies to elucidate solvent dynamical influences on the optical spectra of solvatochromic molecules. The program includes (1) measuring absorption, emission, and resonance Raman spectra in low-temperature glass, in order to isolate the intramolecular contribution to the linewidth, (2) employing solvent isotopomers to isolate solvent dynamical effects on absorption, emission, and resonance Raman spectra in room temperature solvents, and (3) determining fluorescence yields and lifetimes as a function of solvent isotopic substitution in order to obtain radiative and nonradiative decay rates in glass and liquid phase solutions. These strategies will enable the extraction of the solvent-induced dephasing function, and hence the solvent spectral density. Issues to be addressed include the sensitivity of radiative and nonradiative relaxation rates to solvent isotopomer, the validity of treating solvent response as independent of the solute electronic state, the possible dependence of solvent-induced electronic dephasing on vibrational mode, and the role of solvent intramolecular modes in electronic dephasing. Molecules dissolved in liquid solvents exhibit behaviors that are much affected by the solvent molecules in the surrounding environment. These interactions are complex and still not understood well at this time. Results from this project will help to bridge the gap between theoretical predictions and real systems in understanding solution dynamics. Fundamental insights from this work could improve both the description of electron transfer processes relevant to biochemistry and the molecular models for nonlinear optical properties relevant to materials science.