SPECTRAL EVIDENCE FOR DIFFERENT PHASES EXHIBITING THE SHPOLSKII EFFECT IN CONCENTRATED-SOLUTIONS OF PYRENE AND DIBENZOFURAN IN FROZEN N-ALKANES

Concentrated frozen solutions of dibenzofuran in n-heptane and pyrene in n-hexane were investigated by both fluorescence and absorption spectroscopy. At extremely high concentrations or relatively high concentrations and diminished crystallization rates, the "normal" quasiline spectra are replaced by "new" spectra that exhibit quasiline character and that are not due to the formation of microcrystals of the solute. Intensity distribution changes among the vibronic lines involving non totally symmetric vibrational modes in the first electronic transition of the new spectrum have been interpreted as a result of weak interactions between oriented solute molecules. A model of the centers from which these spectra are originating is proposed. It is suggested that the model may provide an alternative interpretation for the occurrence, only at high solute concentration, of quasiline spectra, in the case of aromatics in "unsuitable" frozen n-alkanes. © 1990 American Chemical Society.