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A detailed study of the emission, excitation spectra and fluorescence decay of pyrene adsorbed on silica gel, porous Vycor, alumina, and calcium fluoride is reported. Monomer emission and a longer-wavelength broad-band emission (neither decaying with a single exponential) was observed on silica. The excitation spectrum of the broad-band emitter was red shifted in comparison with the absorption responsible for the monomer emission.These, and other, results are interpreted as indicating the existence of bimolecular ground-state pyrene association.The effect of coadsorbates (glycerol, 1-decanol) was examined. At high coverage the monomer emission decay approaches a single exponential and the long-wavelength emission can be deconvoluted with a double exponential with a negative preexponential term indicating true excimer formation. Adamantanol did not have this effect. A model for the pyrene-silica interaction is proposed to rationalize these and other observations.

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The quantum yield of sensitized photoperoxidation of 2,5-dimethylfuran in oxygen-saturated n-hexane solution has been measured. The sensitizers used were 9-methylanthracene, 9-phenylanthracene, 9,10-dimethylanthracene, 9,10-diphenylanthracene, perylene, pyrene, 1,6-diphenylhexatriene, and rubrene, and the sensitized oxidation quantum yields were found to be 0.97,1.09,1.14,1.20,1.27,0.79,1.02, and 1.20, respectively. The experimental results indicate that singlet molecular oxygen can be produced directly from the oxygen quenching of the lowest excited singlet state of many aromatic molecules, i.e., the process S, + 302 -+ 402 is not negligible when compared to 8 + 302 -* Tx + 302. This shows that the former process must also be taken into consideration in the general treatment of oxygen quenching of the fluorescence from aromatic molecules.

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