ULTRASONIC MODIFICATION OF LIGHT-EMISSION FROM ELECTROCHEMILUMINESCENCE PROCESSES

The influence of ultrasonic irradiation on the electrochemiluminescenc e evolved from the electrochemical oxidation reaction of tris(2,2'-bip yridyl)ruthenium(II) chloride [Ru(bpy)(3)Cl-2] or tris(1,10-phenanthro line)ruthenium (II) chloride [Ru(phen)(3)Cl-2] in aqueous oxalate has been examined. Under the conditions described here, insonation resulte d in an increase in the luminescence yield of over 100%, in a highly r eproducible manner. These effects were found to result from ultrasonic irradiation and can be understood with reference to the changes in ma ss transport of reactants through the bulk solution and modification o f the electrode Nernst diffusion layer that have been observed by othe r workers. A relationship between the light intensity and the square o f the cell current was observed under various ultrasound powers,and it was found that this is consistent with the kinetic scheme proposed by Bard et al. for the electrooxidation reaction under silent conditions . This indicates that the reaction mechanism under insonation is consi stent with that proposed for the silent reaction. The electrochemilumi nescence spectrum under insonation was measured with greater precision than previously and was shown to be identical to that under silent co nditions. Luminescence quenching by oxygen, problematic in earlier rep orts, was measured under insonation and also with greater precision th an previously in the silent system. The Stem-Volmer relationship was o beyed under both sets of conditions, and oxygen quenching phenomena ap pear to be unaffected by insonation of the system.