Spectroscopic Properties of Quercetin in AOT Reverse Micelles†

The spectroscopic properties of quercetin (QCT) were studied in the AOT reverse micelle by fluorescence spectroscopy. Because the molecular structure of QCT is completely planar, excited state intramolecular proton transfer (ESIPT) occurs between the –OH at C(5) and carbonyl oxygen via intramolecular hydrogen bonding. This ESIPT happens at the S1 state but not at the S2 state. Because QCT is a good donor-acceptor-conjugated molecule at the excited state, this molecule can emit strong fluorescence but shows no S1 → So emission due to this ESIPT. Since the S2 → S1 internal conversion was very slow due to the small Franck-Condon factors, S2 → So fluorescence emission was observed. All of the experimental results indicated that the QCT resided at the bound water interface and that the position of solute did not change significantly in the micelle at various water concentrations