Detailed photophysical properties of a functionalized ruthenium(II) polypyridyl complex: through-space solvent effects

Abstract

The synthesis and detailed photophysical properties of a bis(N-methylene-4-pyridinium-4′-pyridine)-functionalized ruthenium(II) polypyridyl complex in solvents of varying polarity and Gutmann's donor number (DN) are reported, along with its single-crystal X-ray structure. The emission spectrum of the complex in varying solvents was also simulated and parameters, including the Huang–Rhys (S_m) electron-vibrational coupling constant, obtained. Reasonable correlations of the optical properties with the solvent polarity factor (Δf) and DN were observed. A difference in dipole moment between the ground and excited states of ca. 10 D was calculated, and a simplified potential-energy surface model proposed to explain the results. Excited state lifetimes in acetonitrile were determined over a modest temperature range of 60 K. The linear Arrhenius plot of ln(k_obs) s. 1/T gave an activation energy of 5.6(±0.6) kJ mol⁻¹, which is low when compared to the literature value of 45.5 kJ mol⁻¹ for [Ru(bipy)₃]²⁺.