ELECTROCHEMILUMINESCENCE IN LOW IONIC-STRENGTH SOLUTIONS OF 1,2-DIMETHOXYETHANE

Steady-state electrochemiluminescence (ECL) arising from ion annihilation reactions was examined at a double-band microelectrode in 1,2-dimethoxyethane (DME) as a function of electrolyte concentration for the following reactions: the 9,10-diphenylanthracene (DPA) radical cation with the DPA, benzil and 2-naphthyl phenyl ketone (NPK) radical anions, and the rubrene radical cation with the rubrene radical anion. The ECL efficiency of all systems was found to increase as the added electrolyte concentration was decreased from 100 to 0.1 mM. These increases were found to correlate with changes in Delta E(1/2) attributed to ion-pairing of the radical ions with their electrolyte counter-ions. For the energy-sufficient ECL reaction of DPA in DME, the increase in the Gibbs energy available for reaction as the electrolyte concentration was lowered produced an ECL efficiency approaching the theoretical limit of 25%.