Photophysical properties of the photosensitizer [Ru(bpy)2(5-CNphen)]2+ and intramolecular quenching by complexation of Cu(II)

The lifetime of the 3MLCT emitting state of [Ru(bpy)2(5-CNphen)]2+ (bpy = 2,2′-bipyridine, 5-CNphen = 5-cyano-1,10-phenanthroline) has been determined in CH3CN by flash photolysis and TCSPC techniques. The obtained value, τ = 2.2 μs, points to its potential use as a photosensitizer in molecular devices. The transient spectrum shows that this excited state can be formulated as a metal-to-ligand charge transfer state. Static and dynamic quenching of the complex luminescence by Cu2+ ions is observed. The static and dynamic components were evaluated by measuring emission intensities and lifetimes at different [Cu2+]. The combined quenching results point to a strong ground state complexation of Cu2+ (Keq = 7500 M−1 for 1:1 complex) with the nitrile group of 5-CNphen. At high [Cu2+], a short-lived component of the decay has been detected, with ket = 4.0 × 109 s−1. This value is compared to the electron transfer rate constant in the encounter complex of the bimolecular quenching, which was obtained from the dynamic quenching rate constant.