The photoperoxidation of unsaturated organic molecules. Intersystem crossing in 9,10-diphenylanthracene

Measurements of the quantum yield of 9,10-diphenylanthracene autoperoxidation as a function of dissolved oxygen concentration in benzene at 25°C are consistent with an intersystem crossing yield of 0.13 ± 0.03 for this molecule and the absence of the spin-allowed exothermic process S₁ + O₂³Σ → T₁ + O₂ Δ. These conclusions indicate the presence of a second triplet state below S₁.