Photophysical induction of dual fluorescence of quercetin and related hydroxyflavones upon intermolecular H-bonding to solvent matrix

Spectroscopic Properties of Quercetin in AOT Reverse Micelles

“…The QCT with the 5-OH group has been known as a nonfluorescent compound in aqueous solutions. [10][11][12] However, it gave new fluorescence emission spectra in various hydroorganic mixed solvents when it was excited to the second excited state under 255 nm light, which corresponded to the maximum absorption of Band II. However, when 370 nm radiation, which corresponded to the maximum absorption of Band I, was used as the excitation source, no fluorescence emission was observed in the same mixed solvents.…”

“…The intramolecular hydrogen bond between 5-OH and O-11, which forms a stable six-membered ring, is stronger than that between 3-OH and O-11. 10,35,[38][39][40] For this reason, the QCT, 5-hydroxyflavone, has a dramatically different excited state behavior from that of 3-hydroxy flavone, which have only the -OH group at the C-3. 10,11 Excited state intramolecular proton transfer (ESIPT) between 5-OH and O-11 by "keto-enol tautomerization" has been observed in 5-hydroxyflavone and other many molecules having this kind of intramolecular hydrogen bond.…”

“…[1][2][3][4][5][6] QCT is remarkable for its properties to mitigate the increase in capillary fragility, to reduce high blood pressure, to protect plants against the direct and indirect influences of UV radiation and to show antioxidant behaviors against a wide range of free radicals. [7][8][9][10][11][12] Flavonoids are well known compounds that exhibit characteristic fluorescence properties. 10,13 QCT has been considered to be composed of a special class of nonfluorescent molecules.…”

“…[7][8][9][10][11][12] Flavonoids are well known compounds that exhibit characteristic fluorescence properties. 10,13 QCT has been considered to be composed of a special class of nonfluorescent molecules. [10][11][12] However, a new significant fluorescence emission was discovered in CH 3 OH-H 2 O and CH 3 CN-H 2 O mixed solvents.…”

“…10,13 QCT has been considered to be composed of a special class of nonfluorescent molecules. [10][11][12] However, a new significant fluorescence emission was discovered in CH 3 OH-H 2 O and CH 3 CN-H 2 O mixed solvents. 14 It would be, therefore, very interesting to study the physicochemical properties of QCT in a specific environment, especially in vivo, to better understand the mechanism of its strong biological activity.…”