EFFECT OF S-1 TORSIONAL DYNAMICS ON THE TIME-RESOLVED FLUORESCENCE-SPECTRA OF 9,9'-BIANTHRYL IN SOLUTION

Time-resolved fluorescence spectra of 9,9'-bianthryl (BA) were measure d in methylcyclohexane (MCH)) and a Decalin-isooctane (D-ISOO) mixture at several temperatures between 127 and 200 K. A suitable choice of t he excitation wavelength makes it possible to observe a maximum manife station of the Sr torsional dynamics. A quantitative simulation of the time-resolved fluorescence spectra could be achieved based on the des cription of the torsional relaxation by a Smoluchowski equation. Besid es, 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 fri ction coefficient zeta shows a power law dependence on the shear visco sity eta, zeta proportional to eta(a), with a = 0.62.