NEW INFORMATION ON THE FLUORESCENCE ENHANCEMENT IN QUINOLINE AND ISOQUINOLINE BY HYDROGEN BONDING SOLVENTS
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Publisher:Ohio State University
It has been known for many years that the fluorescence quantum yield of quinoline and isoquinoline is far larger in a hydrogen bonding solvent than in a non-polar hydrocarbon. Other features of the fluorescence and phosphorescence spectra such as polarization and vibronic activity, and phosphorescence lifetimes have also been found to be quite different in these two types of solvents. Unfortunately, It has been difficult to determine reliable quantum yields of either fluorescence or phosphorescence. In the present work we have been able to show that at least some of the solvent dependent variability is due to impurities. For both molecules we find from studies of the excitation spectra and phosphorescence lifetimes that fluorescence and phosphorescence are coming from two different molecular species. The evidence suggests that hydrogen bonding, even by trace impurities, induces fluorescence, but that most if not all of the phosphorescence comes from non-hydrogen bonded species. The implication of this finding for the theory of intersystem crossing in nitrogen heterocycles will be discussed, and a revised upper limit on the fluorescence quantum yield of non-hydrogen bonded quinoline and Isoquinoline will be presented.
Author Institution: Department of Chemistry, Williams College
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