The spectroscopic and electrochemical properties of a series of four Ru II 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 CH 3 CN 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) , at variance with the electronic structures inferred from the absorption spectra. Nanosecond time-resolved electronic absorption and time-resolved step-scan infrared data are used to resolve this apparent conflict and confirm localization of the long-lived 3 MLCT state on dmb in all three complexes where this ligand is present, thus making the dea-based excited state unique to [Ru-(dea) 3 ] 2+ . Electrochemical studies further reveal the origin of this result, where a strong influence of the dea ligand on the oxidative Ru II/III couple, due to π donation from the diethylamino substituent, is observed. The electronic absorption spectra are then reexamined in light of the now well-determined excited-state electronic structure. The results serve to underscore the importance of complete characterization of the electronic structures of transition metal complexes before embarking on ultrafast studies of their excited-state properties.

A versatile spectroelectrochemical apparatus is introduced to study the changes in IR spectra of organic and inorganic compounds upon oxidation or reduction. The design is based on an attenuated total reflection device, which permits the study of a wide spectral range of 16,700 (600 nm)-250 cm(-1), with a small opaque region of 2250-1900 cm(-1). In addition, an IR data collection protocol is introduced to deal with electrochemically nonreversible background signals. This method is tested with ferrocene in acetonitrile; concentrations as low as 1 mM produce results that agree with those in the literature.