Electrochemiluminescence of 9,10-diphenylanthracene-halogen ion systems

Influence of halide ions (Cl^?, Br^?, I^?) on the electrochemiluminescence (ecl) of 9,10-diphenplanthracene (DPA) is studied by using controlled-potential double-step method. It is confirmed that the ecl begins to appear at the anodic potential corresponding to the potential of the first anodic half-wave potential of each halide ion and that, passing through an intensity maximum, it disappears at more positive potential. Similarly, when the cathodic potential is changed, the ecl appears at the first cathodic half-wave potential of DPA and disappears at more negative potential than the second half-wave potential of DPA. These facts indicate that the ecl must be due to the reaction between oxidised species of halide ions (presumably trihalide ions) and monovalent DPA anion radicals. The mechanism for the formation of the excited singlet state of DPA is reasonably explained by assuming a reaction scheme containing a mono-halogenated DPA radical as an intermediate.