Orientational dynamics of C70 molecules in chlorobenzene

Abstract

Dynamics of anisotropy relaxation of C70 singlet excited molecules in chlorobenzene was measured at room temperature by the picosecond transient grating technique. The time-ependent diffraction efficiency exhibits a two-stage decay: a fast component (τ1 = 12±5 ps), which is comparable with the corresponding signal of C60 in chlorobenzene (τ = 8±2 ps), and a slow one (τ2 = 30±5 ps). It is supposed that relaxation of anisotropy is related to the orientational mobility of excited C70 molecules relative to two axes of the molecular framework. The results obtained cannot be described by the Einstein-Stokes-Debye theory. The Hynes-Kapral-Weinberg theory, which takes into account microscopic interactions between molecules upon collisions, agrees satisfactorily with the experiment. The influence of dielectric friction on the orientational mobility of C70 in chlorobenzene was estimated.