The role of geminate reaction in the self‐sensitized photooxygenation of helianthrene and hetianthrene‐derivatives encounter‐ and reencounter probabilities

Abstract

AbstractThe probabilities pexpRQ of the geminate reaction between singlet oxygen (1Δ) and helianthrene (H), mesodiphenylhelianthrene (MDH) and mesodiphenylbenzhelianthrene (MDBH) were determined in several solvents of different viscosity. pexpRQ strongly depends on the viscosity of the solvent. For H pexpRQ increases from 0.17 (n‐pentane) over 0.44 (benzyl alcohol) to 0.97 (m‐cresol). For the first time experimental results clearly demonstrate that the reaction already takes place in the initial encounter, which is formed in the energy transfer from the T1‐states of the hydrocarbons to molecular oxygen. The solvent dependence of pexpRQ is only caused by the solvent dependence of the total reencounter probability, po. The results permit calculation of the probabilities per encounter (αR) and rate, k01, for an equilibrium distribution of 1Δ and the hydrocarbons.