Photochemistry of the singlet oxygen [O-2((1)Delta(g))] sensitizer perinaphthenone (phenalenone) in N,N '-dimethylacetamide and 1,4-dioxane

1H-Phenalen-1-one (perinaphthenone), an efficient singlet oxygen [O-2((1)De lta(g))] sensitizer with a quantum yield of singlet oxygen production (Phi( Delta)) close to unity, has been proposed as a universal standard for O-2(( 1)Delta(g)) studies. However, data about the photochemical stability of phe nalenone are limited to a few protic solvents. This parameter is of crucial interest for singlet oxygen studies under continuous irradiation over long periods of time. In this contribution, we present experimental results dem onstrating that, despite low quantum yields, significant photochemical deco mposition of phenalenone occurs under steady-state irradiation in air equil ibrated 1,4-dioxane and N,N'-dimethylacetamide (DMA), mainly due to hydroge n abstraction from the solvent by its triplet excited state. Furthermore, s inglet oxygen lifetime measurements as a function of irradiation time and c omparison of the rates of decrease of the steady-state O-2((1)Delta(g)) nea r-infrared (1270 nm) phosphorescence with those of phenalenone disappearanc e have led to the conclusion that at least one of the products formed durin g phenalenone irradiation contributes to singlet oxygen sensitization. Quan tum yields of singlet oxygen production by phenalenone, determined using la ser-induced optoacoustic calorimetry (LIOAC) and time-resolved near-infrare d phosphorescence (TRPD), remain high in 1,4-dioxane and in DMA (0.99 +/- 0 .05 and 0.87 +/- 0.05, respectively), confirming that this compound is a ve ry efficient O-1(2) sensitizer in a large variety of solvents (the Phi(Delt a) value in DMA is the lowest measured so far).