Solvation dynamics in N-methylamides

Solvation times in three homologous amides, N-methylformamide, N-methylacetamide, and N-methylpropionamide, have been detd. from measurements of the dynamic Stokes shift of the fluorescence spectra of two-probe solutes, prodan and coumarin 102. Single-particle reorientation times have also been measured in one of these solvents, N-methylformamide, by using NMR methods. The solvation dynamics are compared to two theoretical models, the simple continuum model and the dynamic MSA model. Although neither model predicts the time dependence of the response satisfactorily, the average solvation times observed are close to the solvent longitudinal relaxation time ({tau}{sub L}) predicted by the simple continuum model. In contrast, the predictions of the dynamical MSA model are approximately 4 times slower than the observed solvation response.