Static and Time-Resolved Spectroscopic Studies of Low-Symmetry Ru(II) Polypyridyl Complexes

Abstract

The spectroscopic and electrochemical properties of a series of four RuII polypyridyl complexes are reported. Compounds of the form [Ru(dmb)x(dea)3-x]2+ (x = 0−3), where dmb is 4,4‘-dimethyl-2,2‘-bipyridine and dea is 4,4‘-bis(diethylamino)-2,2‘-bipyridine, have been prepared and studied using static and time-resolved electronic and vibrational spectroscopies as a prelude to femtosecond spectroscopic studies of excited-state dynamics. Static electronic spectra in CH3CN solution reveal a systematic shift of the MLCT absorption envelope from a maximum of 458 nm in the case of [Ru(dmb)3]2+ to 518 nm for [Ru(dea)3]2+ with successive substitutions of dea for dmb, suggesting a dea-based chromophore as the lowest-energy species. However, analysis of static and time-resolved emission data indicates an energy gap ordering of [Ru(dmb)3]2+ > [Ru(dmb)2(dea)]2+ > [Ru(dea)3]2+ > [Ru(dmb)(dea)2]2+, at variance with the electronic structures inferred from the absorption spectra. Nanosecond time-resolved electronic absorp...