Photochemical Reactions of Aromatic Compunds. XXXI. Exciplex Quenching by Pyridine, Methylated Pyridines, and Methylated Imidazoles and Termolecular Interaction in the Excited Singlet State

Abstract
Pyridine, methylated pyridines, and methylated imidazoles quenched the exciplexes of aromatic nitrile–2,5-dimethylfuran or 2,5-dimethyl-2,4-hexadiene, and the rate constants for the exciplex quenching were obtained. The exciplex quenching by 2-methyl- and 2,6-dimethylpyridines was much less efficient than that by the other quenchers. The exciplex quenching was discussed in terms of the interaction of the n-orbital of the quenchers with the positive charge developed on the electron-donor side of the exciplexes. Curved Stern-Volmer plots were obtained in the quenching of aromatic nitrile fluorescence by 1-methylimidazole and/or 1,2-dimethylimidazole. On the basis of the kinetic results, the mechanism was discussed in terms of a termolecular interaction between excited singlet aromatic nitrile, the methylated imidazole as the π-donor, and the second one as the n-donor.

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