At 298 K in acetonitrile solution, the dihydroxy antimony(V) tetraphenylporphine cation [Sb-V(TPP)(OH)(2)](+) shows an intraligand fluorescence at lambda (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 value 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 follows Stern-Volmer kinetics with high rate constants close to the diffusion-controlled Emit. Based on the observation of the reduced complex [Sb-III(TPP)](+) as a permanent photoredox product, the quenching mechanism can be characterized as a bimolecular electron transfer process involving the lowest excited singlet (pi pi*) state of the [Sb-V(TPP)(OH)(2)](+) cation.