THE EFFECTS OF UNCOMPENSATED SOLUTION RESISTANCE AND RATE OF THE HOMOGENEOUS ELECTRON-TRANSFER REACTION ON ELECTROCHEMILUMINESCENCE TRANSIENTS

In double-step electrochemiluminescence experiments, the luminescence emission transients contain interesting information on the electrode r eactions involved, the coupled mass transport and the homogeneous anni hilation reaction. It was found that the start of luminescence emissio n, following the second potential step, occurs only after a delay of t he order of 100 mu s. The effect of Forster-type energy transfer from the electronically excited molecules to the metal electrode is insigni ficant under the experimental conditions considered. Rather, it is sho wn that this delay is caused by the IR(u) drop, which is closely relat ed to the time constant R(u)C(DL), where R(u) is the uncompensated ele ctrolyte resistance and C-DL is the double-layer capacitance. ECL tran sients generated with the digital simulation technique using this info rmation agree with the experimental transients. The rate constant of t he homogeneous annihilation reaction is derived from such fits.