Reductive fluorescence quenching of the photoexcited dihydroxy antimony(V)tetraphenylporphine cation in acetonitrile solution

At 298 K in acetonitrile solution, the dihydroxy antimony(V) tetraphenylpor phine cation [Sb-V(TPP)(OH)(2)](+) shows an intraligand fluorescence at lam bda (max) = 598 nm with tau (F) = 1.46 ns and a quantum yield of phi (F) = 0.028. While the presence of dioxygen has no significant effect on the valu e of phi (F), the fluorescence is very efficiently quenched by Cl-, Br- I- and SCN- ions. At quencher concentrations below 10(-2) M the reaction follo ws Stern-Volmer kinetics with high rate constants close to the diffusion-co ntrolled Emit. Based on the observation of the reduced complex [Sb-III(TPP) ](+) as a permanent photoredox product, the quenching mechanism can be char acterized as a bimolecular electron transfer process involving the lowest e xcited singlet (pi pi*) state of the [Sb-V(TPP)(OH)(2)](+) cation. (C) 2000 Elsevier Science B.V. All rights reserved.