Viscosity dependence of the rotational reorientation of rhodamine B in mono- and polyalcohols. Picosecond transient grating experiments

Abstract

Rotational reorientation times (Tau/sub ROT/) were obtained for rhodamine B in a series of n-alcohols and polyalcohols of varying viscosities by a transient grating technique. The general trend of the Debye-Stokes-Einstein (DSE) theory was shown to extend to much higher viscosities than previously reported. Detailed analysis of the results suggests that the n-alcohols and polyalcohols provide two distinct hydrodynamic boundary conditions for the rotating species. In the n-alcohols, stick boundary conditions are observed, while the polyalcohols provide approximately slip boundary conditions. The question of a difference in the rotation times for the ground and excited electronic states is addressed and an upper bound is placed on this difference for rhodamine B. 7 figures, 1 table.