Photophysics of 1-hydroxy-9-fluorenone: absence of excited state intramolecular proton transfer reaction

Absorption, fluorescence, fluorescence excitation spectroscopy and time dependence fluorimetric studies of 1-hydroxy-9-fluorenone (1-HFu) and 1-methoxy-9-fluorenone (1-MFu) have been studied in different solvents. Both these molecules exhibit only one small Stokes shifted and similar fluorescence band, even in ultra dry cyclohexane. This suggests that excited state intramolecular proton transfer (ESIPT) reaction is not observed in 1-HFu. The electronic structure calculations were carried out on each species using semi-empirical AM1 and CNDO/S-CI methods, as well as, hybrid density-functional theory (DFT) B3LYP with 6-31 G∗∗ basis set to find out the cause for non-observance of ESIPT in 1-HFu.