Spectral Shifts in the Absorption and Fluorescence of Pyrene under High Pressures

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Abstract
An experimental study of the electronic spectrum of pyrene under high pressures in polymer matrices, mixed crystals, and in the crystalline state is reported. Pyrene concentrations less than 10−2M in plastics show a red shift in the monomer fluorescence, which is slightly larger than that of the Lb absorption band. In plastic samples containing higher concentrations of pyrene the excimer fluorescence appears and reveals greatly reduced intensities upon compression and net spectral shifts, ranging in magnitude between +700 to −400 cm−1 at 25 kbar. The red shifts in the spectra of pyrene molecules in durene and fluorene host matrices are larger than in the plastics for the absorption bands, but comparable for the monomer fluorescence. Pyrene microcrystals show a red shift of ∼2100 cm−1 in the La band and ∼1500 cm−1 in the excimer fluorescence at 25 kbar.