A homologous series of meridionally-coordinated tridentate 2,2':6',2''-terpyridine Re(I) dicarbonyl complexes have been prepared and investigated. The complexes mer,cis-[Re(tpy-κ(3)N)(CO)2(L)](n) (L = Cl(-) (1), OSO2CF3(-) (2), NCCH3 (3), CN(-) (4), NC5H5 (5), PMe3 (6), PEt3 (7), PPh3 (8), P(OMe)3 (9) and P(OEt)3 (10); n = 0 or +1) have been synthesized and characterized by elemental analysis, (1)H NMR and infrared spectroscopy. The electrochemistry of these compounds has been studied and compared to that of other known rhenium compounds using an electrochemical parameterization model. Cyclic voltammetry measurements have shown that the first oxidation of the complexes varies systematically in potential as the ligand L is altered. Many of these one-electron oxidations occur at lower potentials compared to more familiar bidentate diimine Re(I) tricarbonyl complexes. A correlation exists between CO, a strong π-acidic ligand, and deviations of the observed reduction potentials from the calculated values. Many of the complexes absorb light throughout a significant portion of the visible spectrum. Two of these complexes, mer,cis-Re(tpy-κ(3)N)(CO)2Cl (1) and mer,cis-Re(tpy-κ(3)N)(CO)2CN (4), absorb light throughout the entire visible spectrum. Low temperature emission spectra were obtained for the compounds mer,cis-Re(tpy-κ(3)N)(CO)2Cl (1) and mer,cis-[Re(tpy-κ(3)N)(CO)2(P(OEt)3)](+) (10) at 77 K in a 4 : 1 methanol-ethanol glass matrix and give metal-to-ligand charge transfer ((3)MLCT) luminescence. Density functional theory (DFT) calculations of the electronic structure are in good agreement with the experimental data.

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Optical and electrochemical properties of the homoleptic cobalt(III/II) complexes mer,mer- [Co(tpy-κ 3 N,NЈ,NЈЈ)] n+ and mer,mer-[Co(bqp-κ 3 N,NЈ,NЈЈ)] n+ (n = 3+ or 2+) are presented [tpy = 2,2Ј:6Ј,2ЈЈ-terpyridine; bqp = 2,6-bis(8Ј-quinolinyl)pyridine]. Both [Co(tpy) 2 ] 3+/2+ and [Co(bqp) 2 ] 3+/2+ systems have been used to formulate redox-mediator electrolytes for application in dye-sensitized solar-cell (DSSC) devices with the MK-2 dye TiO 2 sensitizer. The [Co(tpy) 2 ] 3+/2+ -based electrolyte shows a slightly higher percentage power-conversion efficiency (η = 4.47 %) in a DSSC device relative to the [Co(bqp) 2 ] 3+/2+ -based electrolyte (η = 3.73 %). Although the [a]