FLUORESCENCE ANISOTROPY DECAYS AND VISCOUS BEHAVIOR OF 2-METHYLTETRAHYDROFURAN

The decay of the fluorescence anisotropy has been measured for solutio ns in 2-methyltetrahydrofuran (MTHF) between -50 and -150 degrees C. S olutes include both neutral species (perylene, tetracene, carbazole) a nd ion pairs (of carbazolyl(-), 1,3-diphenylallyl(-) and its vinylogue s). The results lie between values calculated for ellipsoids using the 'stick' and 'slip' boundary conditions. In some cases, notably peryle ne, two-exponential decay is predicted but not observed, suggesting th at the solvent-solute interaction is comparable with solvent-solvent f orces, contrasting with the hydrogen-bonded solvents used by other wor kers. The data are used to discuss cis-trans photo-isomerisation of di phenylallyl ions and to estimate the viscosity of MTHF, for which meas urements cover eleven orders of magnitude. The Williams-Landel-Ferry ( WLF) equation is obeyed well over the whole range with T-0 = 81 K.