EFFECT OF OXYGEN ON LINKED RU(BPY)(3)(2-VIOLOGEN SPECIES AND METHYLVIOLOGEN - A REINTERPRETATION OF THE ELECTROGENERATED CHEMILUMINESCENCE())

The effect of oxygen on the electrogenerated chemiluminescence (ECL) o f the ruthenium trisbipyridyl-viologen complexes -4'-yl-(CH2)(n)-4,4'- bipyridindiium-1'-methyl)(4+) (n = 1, 2, 3, 5, or 8; R = H or Me) has been investigated. This light emission is shown to occur not from a ML CT excited state localized on an unsubstituted bipyridine ligand as ha d been previously proposed, but from decomposition products formed dur ing the ECL experiments when trace amounts of oxygen are present. Thes e ECL-active species are generated when oxygen reduction products reac t with the pendant viologen to alter or remove this ligand, thereby di sabling the electron-transfer quenching of the excited state by the in tact viologen. Electrolysis and extended ECL experiments with methylvi ologen and the ruthenium-linked viologen compounds verify that a numbe r of products are formed under ECL conditions when oxygen is present i n solution. Some of these products have been identified.