The efficiency of aromatic ketones as singlet-oxygen ('02('Ag)) 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 (Gd) by 1H-phenalen-I-one (1) is close to unity in both polar ( @, , = 0.97zk0.03 in methanol) and non-polar solvents ( @ A = 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 x , A * electronic configurations. The quantum yield of intersystem crossing (cDISc) 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 GIsc of 1 and the efficient energy transfer from its triplet state to molecular oxygen. The Iff-phenalen-1-one (l), 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.Introduction. -Because of the relatively small energy difference between the ground state (' Z;) and the ('A,) excited state of molecular oxygen (94.2 kJ .mol-'), singlet oxygen ('02('Ag)) should be easily produced by energy transfer from the lowest triplet state of most sensitizers to molecular oxygen (Eqn. I). However, only few sensitizers are of practical use for the generation of singlet oxygen, an activated oxidizing species which plays an important role in photo-oxidation reactions (type-I1 photo-oxidation) [ 1-71.

1991 luminescence, fluorescence luminescence, fluorescence (organic substances) K 2540 15 -030 1H-Phenalen-1-one: Photophysical Properties and Singlet-Oxygen Production. -The quantum yields for both the production of singlet oxygen and intersystem crossing of the title compound are close to or equal to unity in polar and nonpolar solvents. -(OLIVEROS, E.; SUARDI-MURASECCO, P.; AMINIAN-SAGHAFI, T.; BRAUN, A. M.; HANSEN, H.-J.; Helv. Chim. Acta 74 (1991) 1, 79-90; Inst. Chim. Phys., Ec. Polytech. Fed. Lausanne, CH-1015 Lausanne, Switz.; EN)