Electrogenerated chemiluminescence of sterically hindered porphyrins in aqueous media

A sterically hindered water-soluble porphyrin, tetrakis(3-sulfonatomesityl) porphyrin (H2TSMP), could form stable radical cation in aqueous media after electrochemical one electron oxidation. The anodic oxidation of H2TSMP in the presence of tripropylamine or C2O42- as a coreactant in aqueous solutio n produces electrogenerated chemiluminescence (ECL) with maxima at 640 and 700 nm. The same emission spectrum of ECL and fluorescence indicates that t he ECL emission is from the singlet state of H2TSMP. The annihilation react ions of ZnTSMP (+) and ZnTSMP (-), which are generated electrochemically, i n CH3CN + H2O (1:1) mixed solution results in an emission which is identica l to the photoluminescence. Protection of the active sites against the nucl eophilic attack of water or OH- by sterical hinderance is a successful stra tegy in designing new ECL-active compounds in aqueous media. Both ECL react ion mechanisms are proposed. (C) 2001 Elsevier Science B.V. All rights rese rved.