Time-resolved determination of the quantum yield of singlet oxygen formation by tetraphenylporphine under conditions of very strong quenching

Time-resolved measurements of the O-2((1)Delta(g)) singlet oxygen luminescence sensitized by tetraphenylporphine (TPP) have been performed in the presence of varying concentrations of the O-2((1)Delta(g)) trap tetramethylethylene (TME). Although the O-2((1)Delta(g)) luminescence signal at 1275 nm is partially overlapped by residual sensitizer fluorescence, we still achieved accurate measurements of lifetimes tau(Delta) of O-2((1)Delta(g)) and quantum yields ea of O-2((1)Delta(g)) sensitization even if tau(Delta) is reduced to about 200 ns. These quantitative measurements (i) yield Q(Delta) = 0.78 +/- 0.04 in air-saturated benzene, which corrects the average Q(Delta) = 0.6 +/- 0.1 of the literature values obtained with this technique but is identical to the value Q(Delta) = 0.80 previously found with TME by the photostationary state method, (ii) confirm that the fraction S-Delta of triplets quenched by O-2 giving rise to O-2((1)Delta(h)) is nearby unity in benzene, and (iii) exclude a relatively long-lived nonluminescent complex being highly reactive toward TME, formed from O-2((1)Delta(g)) and TPP, which was previously proposed, precisely to explain the difference between the values obtained by the two techniques.