Absorption, magnetic circular dichroism and magnetic circular polarization of luminescence studies of Ru(bpy) 2+3 and complexes with a Di(ethoxycarbonyl)-substituted bipyridine ligand as a probe of rigid environments

Abstract

The ruthenium tris(bipyridine)(RBY) chromophore and mono di(ethoxycarbonyl) derivatives have been studied by low temperature absorption, magnetic circular dichroism (MCD) and magnetic circular polarization of luminescence (MCPL) spectroscopy in a range of rigid systems of varying character. These include 4:1 ethanol–methanol glass (EM), poly-(methylmethacrylate)(PMMA), poly(vinyl alcohol)(PVA) and Nafion, a transparent ion exchange medium based on poly(tetrafluoroethane). Absorption and MCD spectra of RBY show some variation in spectral width with medium, but the luminescence and MCPL spectra show more significant variations in position, magnitude and profile as a function of environment. The reduction in MCPL and profile changes in luminescence for RBY in Nafion are taken as evidence for a strong (environmentally induced) distortion in the excited state, giving some degree of localization in this environment. This is matched with the markedly increased photo-chemical activity of RBY in the Nafion environment. MCD spectra of the substituted complexes are markedly different to those of the parent RBY, indicative of a dominant low symmetry potential influencing the metal t⁵₂ core in the excited state. Luminescent states are less (but significantly) affected, indicative of their largely spin-derived magnetic moments.