1H-PHENALEN-1-ONE - PHOTOPHYSICAL PROPERTIES AND SINGLET-OXYGEN PRODUCTION

The efficiency of aromatic ketones as singlet-oxygen (O1(2)(1-DELTA-g)) sensitizers can vary considerably with the electronic configuration of their lowest triplet state and the solvent used. Near-infrared measurements of the luminescence of singlet oxygen have shown that the quantum yield of singlet-oxygen production (PHI-DELTA) by 1H-phenalen-1-one (1) is close to unity in both polar (PHI-DELTA = 0.97+/-0.03 in methanol) and non-polar solvents (PHI-DELTA = 0.93+/-0.04 in benzene). Analysis of the absorption spectra of the ground state and phosphorescence measurements show that the lowest singlet and triplet states have dominant pi,pi-* electronic configurations. The quantum yield of intersystem crossing (PHI-ISC) of 1, determined by laser flash photolysis (partial-saturation method), is equal to unity. In comparison with other aromatic ketones, these parameters are important for the discussion of the surprisingly high PHI-ISC of 1 and the efficient energy transfer from its triplet state to molecular oxygen. The 1H-phenalen-1-one (1), being one of the most efficient singlet-oxygen sensitizers in both polar and non-polar media, could be used as a reference sensitizer, in particular in the area of relatively high energies of excitation.