Ultrafast transient and permanent hole burning and fluorescence line narrowing are used to study the dynamic interaction between the electronic states of a nonpolar solute (dimethyl-s-tetrazine) and its solvent (glycerol) from low temperature glass to room temperature liquid. A model for phonon-modulated interactions not only describes the glass phase results, but also extrapolates to describe the short time dynamics in the liquid phase. However, this mechanism does not account for all of the ultrafast interaction seen at room temperature. A second mechanism connected to the structural coordinates of the liquid is identified. It has a strongly temperature dependent relaxation rate, which becomes subpicosecond at room temperature. This mechanism's rate is significantly faster than rates measured by other structural relaxation experiments.
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