Photochemical dimerization of flavones

Abstract

Photochemical Dimerization of Flavones.

Photochemistry of Flavonoids

“…Yokoe and co-workers [ 48 ] obtained similar results. Photolysis (450 W high pressure mercury lamp, Pyrex filter) of flavone 44 in a methanol-water solution in the presence of sodium sulphite yielded meso -2,2'-biflavanone 45 and (+/-)- meso -2,2'-biflavanone 46 .…”

pH-Dependent fluorescence spectroscopy. Part 12. Flavone, 7-hydroxyflavone, and 7-methoxyflavone

“…The finding, that flavone, like chromone =p3O or xanthone,31 is non-fluorescent in neutral solution is in contradiction to reports which claim it to be fluorescent a or even strongly fluorescent.= The lack of fluorescence in ethanol has been explained on the basis of the El Sayed selection rule by efficient intersystem crossing to the well characterised flavone triplet ~t a t e , ~J ~J ~~ which may be responsible for its photoreactivity. 22 It is evident from the lack of fluorescence and the identity of the pK, values obtained by absorption and fluorescence measurements, that the rate of adiabatic protonation of S, flavone is too slow to compete successfully with intersystem crossing.…”

A laser flash photolysis and theoretical study of hydrogen abstraction from phenols by triplet α-naphthoflavone

“…3,4 Photophysical and photochemical studies on flavonoids have revealed important properties of these substances, and photodimerization is the principal photochemical reaction of flavone in 2-propanol. 5 Time-resolved spectroscopy experiments suggest that flavone photochemistry is mainly mediated by the triplet excited state, 6,7 as confirmed by the high intersystem crossing (ISC) quantum yield (B0.9). 8 The transient absorption spectrum of triplet flavone shows bands at 365-370 nm and 640-650 nm, and this transient has been shown to be reactive towards hydrogen donors.…”