The effect of solvent environment on molecular electronic transition moment directions: Symmetry lowering in pyrene

Measurements of polarized fluorescence and phosphorescence of pyrene, 2-fluoropyrene, and 2-methylpyrene in 3-methylpentane glass at 77 K reveal significant differences among the three molecules. These are interpreted in terms of solvent-induced mixing of the Lb and La states. It is proposed that such symmetry-lowering effects of the solvent environment may well be important contributors to the often observed discrepancies between the theoretical limiting values of polarization ratios and the values actually observed.