Proton-Transfer Spectroscopy of 3-hydroxyflavone in an Isolated-Site Crystal Matrix

The isolated-site low-temperature crystal matrix (dilute solutions in heptane and in octane) (Shpol'skii matrix) is shown to be operative for the spectroscopic study of 3-hydroxyflavone luminescence. The observed luminescence is demonstrated to be unique proton-transfer fluorescence from the excited tautomer. A separate study at higher concentrations of aggregated molecule luminescence and excitation spectra distinguishes these for 3-hydroxyflavone from isolated-molecule spectra. The application of the Shpol'skii matrix low-temperature spectroscopy technique is suggested for other large heteroaromatic molecules, such as biomolecules containing polar groups that impart low solubility in nonaqueous solvents.