Fluorescent behaviors and reaction mechanism of 10-hydroxybenzo[h]quinolone on the detection of phenylboronic acid

The fluorescent behaviors and reaction mechanism of 10-hydroxybenzo[h]quinolone (HBQ) on the detection of phenylboronic acid (PBA) have been theoretical studied. The potential curves scan of HBQ in the first single (S1) excited state indicates that the enol form transfers to keto form without any energy barrier. This enol→keto transfer is induced by excited state intramolecular proton transfer (ESIPT) in the S1 state, which occurs in 50 fs with fluorescence emission located at 615 nm. The fluorescence peak of hydrogen bonded HBQ-PBA blue-shifts about 25 nm compared to monomer HBQ dues to the formation of intermolecular hydrogen bond. Thereafter the intermolecular hydrogen bond interrupts the ESIPT and forms reaction products of benzo[h]quinolin-10-yl hydrogen phenylboronate (BQHP) and water. The result of nonadiabatic dynamics indicates that the internal conversion of BQHP complex is forbidden and the fluorescence emission is the main decay pathway. The BQHP exists a fluorescence emission located at 564 nm (S1), which blue-shifts about 50 nm compared with that of intermediate of HBQ-PBA. This work provides a reasonable mechanism of HBQ on the detection of phenylboronic acid.