ABSORPTION AND FLUORESCENCE SPECTRA OF FLAVONOLS

Absorption and fluorescence spectra of a number of flavonols (with 4'-OCH₃ or 4'-OCH₂ \(\phi\) substitution) and flavonol-acetates have been reported and discussed. The additional absorption band in flavonol and its derivatives is due to keto-enol tautomerism. 4'-OCH₂R (R=H,\(\phi\))  of group produces a bathochromic effect which is due to the increase in resonance by this substitution. Benzoyl group in 6- position modifies the spectrum radically, while conversation of 3-OH to 3-O.CO.CH₃ reverts the spectrum to that of flavone.

Fluorescence spectrum of flavonols has two bands in the visible. 4'-OCH₃ and 4'-OCH₂\(\phi\) groups increase and bensoyl group greatly reduces the fluorescence efficiency. Acetylation of the hydroxyl at 3- position tends to revert the fluorescence spectrum to that of flavone, but there is a considerable decrease in efficiency.