Intramolecular hydrogen bonding. 2. Enormous deuterium isotope effect on the phosphorescence of 6-hydroxybenzanthrone

Abstract

The laser-excited fluorescence and phosphorescence spectra of the title compound and its hydroxy-deuterated analogue have been measured in an n-hexane Shpol'skii matrix at 10 K. The deuterium substitution has only a minor effect on the fluorescence intensity and the fluorescence and phosphorescence vibronic patterns but leads to a greater than order of magnitude increase in the phosphorescence quantum yield. The phosphorescence lifetimes have been measured to be 19 ms for the normal isotopic species and 300 ms for the deuterated form. This probably represents the largest deuterium isotope effect yet observed in aromatic molecule photophysics.