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Abstract
The fluorescence enhancement, which has been reported only for naphthanthrone, was also observed in benzanthrone, 3-nitrobenzanthrone, and 2-nitronaphthanthrone in degassed solution irradiated with strong light. These molecules exhibiting the enhancement were non fluorescent, or rather phosphorescent. Therefore, it was confirmed that the fluorescence enhancement is a general phenomenon occurring in phosphorescent molecules and that the enhancement arises from a reaction via their triplet state. The finding that 3-nitrobenzanthrone, known as a potent mutagen, showed significant fluorescence enhancement, suggests a practical application of the enhancement to fluorescence spectroscopic analysis for mutagenic nitrated aromatic compounds that hardly fluoresce. On the association model the fluorescence enhancement is caused by an association complex, which has never been identified experimentally. The existence of the complex was proved by the HPLC chromatography for an ethanol solution of naphthanthrone which had exhibited fluorescence enhancement.
Acknowledgments
This work was supported in part by KAKENHI (21550025) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. The authors are grateful to Dr. Atsuko Nishigaki for her technical assistance in the HPLC analysis.