Effect of S₁ Torsional Dynamics on the Time-Resolved Fluorescence Spectra of 9,9‘-Bianthryl in Solution

Abstract

Time-resolved fluorescence spectra of 9,9‘-bianthryl (BA) were measured in methylcyclohexane (MCH) and a Decalin−isooctane (D−ISOO) mixture at several temperatures between 127 and 200 K. A suitable choice of the excitation wavelength makes it possible to observe a maximum manifestation of the S 1 torsional dynamics. A quantitative simulation of the time-resolved fluorescence spectra could be achieved based on the description of the torsional relaxation by a Smoluchowski equation. Besides, the band shape analysis enabled the determination of the effective S 1 torsional potential as well as the temperature dependence of the friction coefficient related to the internal torsional motion. The friction coefficient ζ shows a power law dependence on the shear viscosity η, ζ ∝ η a, with a = 0.62.