Temperature-dependent ultrafast solvation dynamics in a completely nonpolar system

Abstract

Transient hole burning measurements on dimethyl-s-tetrazine in n-butylbenzene are reported from the low-viscosity room-temperature liquid down to the low-temperature glass. The results give a detailed picture of the solvation of a nonpolar solute in a nonpolar solvent. The dynamics separate into a phonon modulated and a structural component, as was found previously for polar solvents. The structural component is frozen in the glass, but its relaxation rate increases into the subpicosecond range with increasing temperature. The time decay of the structural relaxation is highly nonexponential. The coupling of the solute electronic state to the structural coordinates is close to linear, but the coupling to the phonon coordinates cannot be accounted for by simple linear or quadratic coupling models. Effects are also found that are attributed to changes in coupling constants with changing density.