The synthesis and properties of several complexes of Ru(II) containing 4,4′-dicarboxy-2,2′-bipyridine (dcbpyH 2 ), 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (bmipy), or 2,6-bis(1-methylbenzimidazol-2-yl)-4-phenylpyridine (phbmipy), and monodentate ligands (X -) Cl -, I -, NCS -, NCSe -, CN -) are reported. The introduction of the ambident ligands X -) NCS -, NCSe -, and CNinto the coordination sphere of [Ru(bmipy)(dcbpy)I] -and cis-Ru(dcbpyH 2 ) 2 Cl 2 has been studied in situ via 1 H and 13 C NMR spectroscopy using 13 C-enriched ligands X -. Introduction of thiocyanate and selenocyanate initially yields the two possible linkage isomers in comparable amounts; prolonged reaction time converts the S-bound isomer and the Se-bound isomer to the N-bound isomers. The isoselenocyanate complex decomposes rapidly, yielding the cyano complex under loss of Se. The N-bound isothiocyanato complex K[Ru(bmipy)(dcbpy)(NCS)] was found to be an efficient sensitizer for nanocrystalline TiO 2 ; the incident monochromatic photon-to-current efficiency (IPCE) is nearly quantitative at 520 nm. Introduction of a phenyl group in the 4-position of the 2,6-bis(1-methylbenzimidazol-2-yl)pyridine ligand gives a red-shifted absorption maximum for the corresponding phenylated K[Ru(ph-bmipy)(dcbpy)(NCS)] complex with an increased molar absorption coefficient for the MLCT maximum at 508 nm. At longer wavelengths above 620 nm, phenyl substitution does not enhance the absorption coefficients of the complex. Compared to that of K[Ru(bmipy)-(dcbpy)(NCS)], the performance of the phenylated complex is reduced in a solar cell due to lower IPCE values. The visible spectra of the halide complexes K[Ru(bmipy)(dcbpy)X] (X -) Cl -, I -) show enhanced red response, but the complexes exhibit strongly reduced overall IPCE values. A comparison of the complexes to cis-Ru-(dcbpyH 2 ) 2 (NCS) 2 is presented. Possible strategies for the design of more efficient sensitizers are discussed.

The photovoltaic stability of RuII(LH2)2(NCS)2 (where LH2 = 2,2′‐bipyridyl‐4,4′‐dicarboxylic acid), a potential sensitizer for solar cells based on anatase, is examined. Its suitability for this role is demonstrated by a 7000 h endurance test, at the end of which no discernible signs of degradation can be detected. An explanation for its remarkable stability of provided by an investigation of its photo‐ and thermally induced reactions in alcoholic solution. Recommendations as to how to avoid ligand substitution reactions that may be undesirable for certain applications are also made.

A series of Ru-polypyridine dyes has been studied with electron spectroscopy using AlKα and synchrotron radiation. Both pure complexes and complexes adsorbed on nanostructured TiO2 (anatase) surfaces have been examined and special emphasis was given to the dye complex cis-bis(4,4′-dicarboxy-2,2′-bipyridine)-bis-(isothiocyanato)-ruthenium(II) [Ru(dcbpy)2(NCS)2]. The measurements provide information concerning the energy level matching between the dyes and the TiO2, which is of importance in photoinduced charge transfer reactions and in applications such as dye-sensitized solar cells. The measurements also support the general picture of bonding of carboxylated complexes to the surfaces via the carboxyl groups of a single bi-isonicotinic acid ligand, and that, for Ru(dcbpy)2(NCS)2, the NCS-ligand–TiO2 interaction is small. Corroborative support is provided via quantum chemical calculations on the ligand (bi-isonicotinic acid) adsorbed on a TiO2 anatase (101) surface.

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