RADIATIONLESS TRANSITIONS IN QUINOLINE AND ISOQUINOLINE VAPORS
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Date
1978
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Ohio State University
Abstract
The emission spectra of quinoline and isoquinoline have been investigated in the vapor phase at room temperature. An effective quenching of $S_{2}(\Pi \Pi^{*}) \rightarrow S_{O}$ fluorescence (resonance fluorescence) of isoquinoline by high pressure buffer gas ($\sim$ 1000-2000 Torr) indicates that the $S_{2}(\Pi \Pi^{*}) \rightarrow S_{1} (n \Pi)$ internal conversion from low vibrational levels in $S_{2}$ is collision-ally induced. The excitation energy dependence of the quantum yield of $S_{2}(\Pi \Pi^{*})$ fluorescence suggests that an irreversible $S_{2}(\Pi \Pi^{*}) \rightarrow S_{1}(n \Pi^{*})$ internal conversion takes place effectively from higher vibrational levels of $S_{2}$. The vibrationally excited $S_{1}$ produced by internal conversion from $S_{2}$ must decay primarily by $S_{1} \rightarrow S_{O}$ internal conversion since the quantum yield of triplet formation, monitored by the sensitized phosphorescence of biacetyl, exhibits a sharp decrease with increasing excitation energy. Qutnoline vapor shows $T_{1}(\Pi \Pi^{*})\rightarrow S_{O}$ phosphorescence as well as $S_{1}(n\Pi^{*})\rightarrow S_{O}$ fluorescence. The excitation energy dependence of fluorescence and phosphorescence quantum yields indicates that the internal conversion is also a prominent radiationless process in this molecule.
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Author Institution: Department of Chemistry