Triplet state properties of pyridine derivatives

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Abstract
The phosphorescence and zero‐field splittings have been systematically investigated for a number of methyl, amino, and cyano derivatives of pyridine in both the neutral and protonated forms. In pyridinium and the methylpyridines, decay from the triplet state appears to have mechanisms similar to those in benzene. Interaction of lowest ππ* triplets with low‐lying 3nπ* states appears to have little effect on zfs, but nonradiative decay rates are distinctly affected. Cyanopyridines and aminopyridines offer less of a comparison to pyridinium. An nπ*‐type configuration may contribute to large D′s for protonated cyanopyridines. Charge‐transfer effects are large in 4‐aminopyridine, although the 2‐ and 3‐aminopyridines apparently do not show significant charge‐transfer character.