Mechanism on the Efficient Formation of Singlet Oxygen by Energy Transfer from Excited Singlet and Triplet States of Aromatic Hydrocarbons

Abstract
The formation efficiencies of singlet oxygen for the oxygen quenching in excited singlet of aromatic hydrocarbons; A and for the quenching in the triplet T1; B were estimated. The hydrocarbons were classified into three types: (i) A = 1 and B = 1 for dicyanoanthracene i.e., total 200% efficiency, (ii) A ≈ 0.3 and B = 1 for anthracene, (iii) A ≈ 0 and B = 1 for pyrene, as examples. It is suggested that the energy levels of T2 and a dissociative exciplex; (T11Δg) correlated to A and B values from the energetic considerations.