PROXIMITY EFFECTS ON THE PHOSPHORESCENCE OF PYRAZINE AND SOME OF ITS DERIVATIVES

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1977

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Ohio State University

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Very efficient radiationless transitions can result when the Lowest excited $n\Pi^{*}$ and $\Pi\Pi^{*}$ states of the same multiplicity are close in energy. We have examined pyrazine (P), 2-methylpyrazine (2-MP) and 2,6-dimethylpyrazine (2,6-DMP) and found strong evidence for this proximity effect. Methylation decreases the $^{3}n\Pi^{*}-^{3}\Pi\Pi*$ energy gap and affects the phosphorescence in two ways: (1) the non-radiative decay rate of the $^{3}n\Pi^{*}$ state greatly increases (Table 1); (2) the vibronic activity of the out-of-plane modes greatly increases, as is seen in the phosphorescence spectra in polycrystalline methylcyclohexane at $4.2^\circ K$. [FIGURE]

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Author Institution: Department of Chemistry, Wayne State University

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