The balance between charge transfer and non-charge transfer pathways in the sensitization of singlet oxygen by pi pi* triplet states.
A charge transfer (CT) channel and a non-CT deactivation channel, both leading to formation of O(2)((1)Sigma (g)(+)), O(2)((1) Delta(g)) and O(2)((3)Sigma(g)(-)), compete in the quenching of triplet states by O(2). Recent studies by our group demonstrated that these channels are described by rather simple and general quantitative relations. In the present paper we use the detailed kinetic data on the quenching by O(2) of pi pi* triplet sensitizers of three homologous aromatic series in CCl(4) to derive a parameter, which describes the balance between CT and non-CT deactivation. This quantity, p(CT), is the relative contribution of CT mediated deactivation and is easily calculated for a sensitizer of known triplet energy from its quenching rate constant. The parameter p(CT) quantitatively describes the balance between both deactivation channels without requiring any knowledge of oxidation potentials. It is shown how the variation of p(CT) influences the efficiencies and the rate constants of O(2)((1)Sigma(g)(+)), O(2)((1)Delta(g)) and O(2)((3)Sigma(g)(-)) formation in the quenching process.
Schmidt
Reinhard
R
Institut für Physikalische und Theoretische Chemie, Johann Wolfgang Goethe-Universität, D60439 Frankfurt am Main, Germany. R.Schmidt@chemie.uni-frankfurt.de
D002251:Carbon Tetrachloride / Q000737:chemistry; D006841:Hydrocarbons, Aromatic / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D010777:Photochemistry; D026082:Singlet Oxygen / Q000737:chemistry*; D013816:Thermodynamics
D006841:Hydrocarbons, Aromatic; D026082:Singlet Oxygen; D002251:Carbon Tetrachloride