Thermal Motion of Prolate Luminescent Molecules in Solvents with Different Viscosities

Abstract

The emission anisotropies r of the fluorescence of the prolate molecules 4-dimethylamino-4′-nitrostilbene (DNS) and 4-amino-4′-nitrostilbene (ANS) in solvents of different viscosities η were investigated. The non-linear dependence of 1/r on T/η was confirmed. Agreement between the experimental data and theory was obtained by the assumption that the prolate luminescent molecules perform irregular rotational motions within a limited solid angle. The theory developed for prolate molecules with the emission transition moment parallel to the long axis of the molecules describes well the experimental results. Rotational relaxation times in different solvents and effective volumes of the studied molecules were obtained.