| Abstrakt: |
The electrochemical and photophysical properties of a series of Ru(II) complexes related to [Ru(dcbpyH2)2(ppy)]1+(1; dcbpyH2= 4,4′-dicarboxy-2,2′-bipyridine; ppy = 2-phenylpyridine) were examined to elucidate the effect of modifying the anionic fragment of the C∧Nligand with conjugated substituents (R). Included in this study is a family of compounds (2−5) consisting of one or two −NO2groups installed meta, ortho, and parato the organometallic bond. A suite of compounds with electron-donating and withdrawing groups (e.g., R = −F (6), −phenyl (7), −4-pyridine (8), −thiophene-2-carbaldehyde (9)) were also evaluated. Deprotonated forms of select compounds were isolated as tetrabutylammonium salts to benefit solution studies. All complexes were structurally characterized by a combination of mass spectrometry, 1H and 13C NMR spectroscopy, and/or elemental analysis. The electronic absorption spectra for all of the compounds reveal three broad bands over the 350−700 nm range. The maximum wavelength of the lowest energy absorbance bands for complexes modified with electron-withdrawing groups are hypsochromically shifted up to 45 nm relative to 1; the weakly emitting compounds (i.e., 1, 3, 6−9) display a hypsochromic shift of up to 63 nm compared to 1. Emission was not observed in cases where the −NO2group was positioned metato the Ru−C bond. The sensitivity of the oxidation potentials to the nature, number, and position of the electron-withdrawing/-donating substituents for the entire set of compounds reflect a highest occupied molecular orbital (HOMO) character extended over the metal, the anionic portion of the C∧Nligand, and, in the case of 7−9, the conjugated R group. The reduction potentials indicate that the lowest unoccupied molecular orbital (LUMO) is localized to the C∧Nligand where R = −NO2, and on the dcbpyH2ligands for all other compounds. This assessment was corroborated by time-dependent density functional theory (TD-DFT) studies. |
