An efficient fluorescence sensor for superoxide with an acridinium ion-linked porphyrin triad.

Addition of potassium superoxide with 18-crown-6 ether (KO(2)(•-)-18-crown-6) to a toluene solution of an acridinium ion-linked porphyrin triad (Acr(+)-H(2)P-Acr(+)) resulted in a remarkable enhancement of the fluorescence intensity. Thus, Acr(+)-H(2)P-Acr(+) acts as an efficient fluorescence sensor for superoxide. Electron transfer from KO(2)(•-)-18-crown-6 to the Acr(+) moiety to produce the two-electron-reduced species (Acr(•)-H(2)P-Acr(•)) results in inhibition of the fluorescence quenching via photoinduced electron transfer, as revealed by laser flash photolysis measurements.