Electrogenerated chemiluminescence from the tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) complex

Electrogenerated chemiluminescence (ECL) from the electron transfer reaction between the reduced and oxidized forms of the tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) complex (Ru(dph)32+) has been studied in butyronitrile. The temperature dependence of the ECL efficiency (φECL in the range 0.18 – 0.33) and that of the luminescence quantum yield of Ru(dph)32+ (φ0 in the range of 0.25 – 0.45) have been investigated. With these quantities the lowering of the efficiencies of the excited state formation with temperature (φes in the range of 0.60 – 0.80) has also been estimated. Based on these results, the ECL mechanism is discussed in terms of Marcus theory, taking into account the vibrational excitation of the reaction products. Differences in the ECL behaviour (temperature dependence on φECL) of the Ru(dph)32+ and Ru(2,2′-bipyridine)3 2+ complexes have been explained using the Jortner formalism for electron transfer reactions in the inverted Marcus region.