Fluorescence studies of excited state intramolecular proton transfer (ESIPT) in molecules isolated in solid argon: 3-hydroxyflavone and 2,5-bis(2-benzoxazolyl)hydroquinone

The fluorescence properties of 3-hydroxyflavone and 2,5-bis(2-benzoxazolyl)hydroquinone were investigated in solid Ar matrixes at 15 K. In both cases dominant emission from the tautomeric form of the mols. was obsd. The excitation spectra of this fluorescence and a weak fluorescence at shorter wavelength showed that the latter is due to mols. with a different ground state, presumably dimers or conformers lacking an internal H bond. For both mols. no fluorescence from the normal form was found, indicating the absence of a barrier to ESIPT