Electrogenerated chemiluminescence (ECL) studies have been performed for the iridium(III) cyclometalated L2Ir(acac) complexes in 0.1 M (n-C4H9)(4)NPF6 acetonitrile-dioxane (1:1, v,v) solutions using a triple-potential-step technique. Electron transfer between electrochemically generated L(2)lr(acac)(+) cations and A(-) (radical anions of aromatic nitriles) leads to generation of the excited 3* L2Ir(acac) species. Extremely high ECL efficiencies (up to 0.55) close to the excited (L2Ir)-L-3*(acac) luminescence yields have been found. © 2004 Elsevier Ltd. All rights reserved.