ABSORPTION AND FLUORESCENCE SPECTRA OF FLAVONES

Absorption and fluorescence spectra of 4'-methoxyflavones with methyl and benzoyl substitutions and 4'-benzyloxyflavones with methyl and methoxy substitutions are reported and discussed. Additional resonance due to a 4'-methoxy group in flavones results in a red-shift of the flavone spectrum. Introduction of methyl groups produces a slight bathochromic effect. Benzoyl substitution in 6-position increases conjugation to a large extent, and the possibility of additional resonance causes a radical change in the spectrum. The behaviour of 4-berizyloxy substitution is not very much different from a 4'-methoxy, except in the high-frequency region. Introduction of methyl groups or replacement of 4' methoxy by 4'-benzyloxy increases the fluores­cence efficiency slightly. 6-Benzoyl group shifts the fluorescence maximum to red and causes a sharp fall in efficiency. A very large increase in efficiency by the introduction of 6-Me, 3'-OMe or 7 :3'- dimethoxy groups in 4'-benzyloxyflaione is observed. A solvent effect in the fluorescence of Savories (not 3-OH derivatives, i.e. flavonols) has been observed in as much as the quantum efficiency increases considerably when the proportion of water in the EtOH-water solvent pair is increased. The effect is observable by qualitative methods and may prove of importance in identification of Savories (Flavonols and isomeric benzylidene-courmaranones do not behave in this manner)