TIME-RESOLVED NONPOLAR SOLVATION DYNAMICS IN SUPERCOOLED AND LOW-VISCOSITY N-BUTYLBENZENE

We have measured the time-resolved dynamics of the structural solvation of dimethyl-s-tetrazine in n-butylbenzene, a completely nonpolar system. A combination of transient hole burning and time-resolved fluorescence has been used to measure Stokes shift dynamics from 155-250 K, spanning a viscosity range of 6.6 X 10(5)-2.5 cP. The decays have a nonexponential shape that is well described by a stretched exponential with beta is similar to 0.5. The time constants for solvation are equal to the shear relaxation times derived from viscosity and ultrasound measurements, suggesting that mechanical relaxation of the solvent is of prime importance in the structural solvation of nonpolar electronic states. A potential correlation with solute rotational dynamics is argued to be less plausible, based on the small size of the implied hydrodynamic volume.