PHOTOPHYSICAL INDUCTION OF DUAL FLUORESCENCE OF QUERCETIN AND RELATEDHYDROXYFLAVONES UPON INTERMOLECULAR H-BONDING TO SOLVENT MATRIX

Quercetin (3,3',4',5,7-pentahydroxyflavone) in contrast to many hydrox yflavonols exhibits very Little or no fluorescence in 298 K liquid sol ution or in the rigid glass protic solvents at 77 K. However, in the W beam of the spectrofluorimeter a strong dual fluorescence builds up i n a protic solvent on a time scale of 5-30 min. This is demonstrated t o be a photophysical induction of fluorescence in the thermally anneal ed solvent matrix at 77 K. The 5-OH group in the vibrationally excited molecule can execute a motion converting its H-bond from an intramole cular to an intermolecular one, activating the 5-OH intramolecular pro ton transfer fluorescence. (C) 1998 Elsevier Science B.V. All rights r eserved.