Efficiencies of singlet oxygen production and rate constants for oxygen quenching in the S1 state of dicyanonaphthalenes and related compounds

Abstract

The quantum yield of singlet oxygen (¹O₂ (¹Δ_g)) production (Φ_Δ) in the oxygen quenching of photoexcited states for 1,2-dicyanonaphthalene (1,2-DCNN), 1,4-dicyanonaphthalene (1,4-DCNN) and 2,3-dicyanonaphthalene (2,3-DCNN) in cyclohexane, benzene, and acetonitrile was measured using a time-resolved thermal lens (TRTL) technique, in order to determine the efficiency of singlet oxygen (¹Δ_g) production in the first excited singlet state (S₁), (f_Δ^S). The efficiencies of singlet oxygen (¹Δ_g) production from the lowest triplet state (T₁), (f_Δ^T), were nearly unity for all DCNNs in all the solvents. The values of f_Δ^S were fairly large for 1,2-DCNN (0.33–0.57) and 1,4-DCNN (0.33–0.66), but were close to zero for 2,3-DCNN. Rate constants for oxygen quenching in the S₁ state (k_q^S) obtained for these compounds were significantly smaller than diffusion-controlled rate constants. The kinetics for processes leading to production and no production of singlet oxygen is discussed on the basis of the values of f_Δ^S and k_q^S. The results obtained regarding phenanthrene (PH), 9-cyanophenanthrene (9-CNPH), pyrene (PY) and 1-cyanopyrene (1-CNPY) are also discussed.