Photoprocesses in Diphenylpolyenes. 3. Efficiency of Singlet Oxygen Generation from Oxygen Quenching of Polyene Singlets and Triplets

Article abstract of DOI:10.1021/j100250a022

The efficiencies of singlet oxygen (¹O₂^*) photogeneration from the oxygen quenching of the excited states (singlet/triplet) of retinal-related polyenals and diphenylpolyenes have been measured in cyclohexane and methanol by 337.1-nm laser flash photolysis.The ¹O₂^* yields are essentially quantitative with all-trans-retinal and its lower and higher homologues as triplet photosensitizers.For all-trans-1,6-diphenyl-1,3,5-hexatriene (DPH) and all-trans-1,8-diphenyl-1,3,5,7-octatetraene (DPO), both singlet and triplet quenching by oxygen contribute to the formation of ¹O₂^*; significant fractions (0.1-0.7) of the oxygen-induced intersystem crossing in these polyene systems take place without energy transfer to oxygen.The triplet-mediated ¹O₂^* yield obtained by steady-state photolysis of all-trans-1,4-diphenyl-1,3-butadiene (DPB) under energy-transfer sensitization by pyrene-1-aldehyde in O2-saturated benzene is less than unity (0.7 +/- 0.1), suggesting possible fractional quenching by oxygen at an orthogonal geometry of DPB triplet (responsible for "nonproduction" of ¹O₂^*).