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 have been investigated in solid argon matrices at 15 K. In both cases dominant emission from the tautomeric form of the molecules is observed. The excitation spectra of this fluorescence and a weak fluorescence at shorter wavelength show that the latter is due to molecules with a different ground state, presumably dimers or conformers lacking an internal hydrogen bond. For both molecules no fluorescence from the normal form is found indicating the absence of a barrier to excited state intramolecular proton transfer (ESIPT).