Picosecond reorientational dynamics of oppositely charged dye molecules. Correlation with the dielectric friction
The rotational reorientation times (τrot) of charged dyes have been measured in polar protic and aprotic solvents, using difference frequency modulation picosecond pump-probe spectroscopy. The dielectric friction (DF) model has been shown to explain nonhydrodynamic behavior in alcohols and alcohol/water mixtures but is unsuccessful in predicting observed differences between the dye molecules in other solvent systems. These deviations are correlated with specific solvation interactions for cations in some solvents.