| Abstract
| - The preparation and the properties of several ruthenium complexes of the general formula cis-RuL2X2 with L =2,2‘-bipyridine-4,4‘-bisphosphonic acid, L‘ = 2,2‘-bipyridine-5,5‘-bisphosphonic acid, and X = Cl, CN, or NCS arereported. The synthesis of these complexes relies on the preparation of the key intermediates cis-Ru(bipyridinebis(diethyl ester phosphonate))Cl2. The ground-state second pKa values of the thiocyanato complexes were determinedand are 6.0 and 6.1 for cis-RuL2(NCS)2 and for cis-RuL‘2(NCS)2, respectively. For these species, 13C NMR and IRdemonstrate that the thiocyanato ligands are bound to Ru via the N atom. The new complexes exhibit a blue-shifted electronic absorption spectrum with respect to the analogous complexes containing carboxylic acid groups.Density functional theory molecular orbital calculations show that the LUMO of the bipyridine phosphonated ligandsis at higher energy than the corresponding dicarboxylate complexes and that the thiocyanato ligands are not simplespectator ligands, whose role is to enrich electron density on the ruthenium, but are also involved in transitionsfrom Π*Ru−NCS to Π*bpy that extend the absorbance of the dye in the low energy part of the absorption spectrum.The photoaction spectra recorded in a sandwich regenerative photovoltaic cell indicate that the cyano and thiocyanatocomplexes containing the bipyridine substituted in 4,4‘ positions exhibit a 90−95% photoconversion efficiency onthe MLCT band, whereas those containing the bipyridine substituted in 5,5‘ positions display lower efficiency (60−65%). The most efficient complex in the series is cis-RuL2(NCS)2; however, its overall efficiency is about 30%lower than the analogue cis-Ru(H2dcb)2(NCS)2 (H2dcb = 2,2‘-bipyridine-4,4‘-dicarboxylic acid) due to a lowerabsorbance in the red part of the visible spectrum.
- The preparation and the properties of several ruthenium complexes of the general formula cis-RuL2X2 with L = 2,2‘-bipyridine-4,4‘-bisphosphonic acid or with L‘ = 2,2‘-bipyridine-5,5‘-bisphosphonic acid and with X = Cl-, CN- or NCS- are reported. Electronic absorption and emission spectra along with the cyclic voltammograms of these complexes were recorded. The photoaction spectra recorded in a sandwich regenerative photovoltaic cell indicate that the most efficient complex in the series is cis RuL2(NCS)2, however its overall efficiency is about 30% lower than the analog cis Ru(H2dcb)2(NCS)2 (H2dcb = 2,2‘-dipyridine-4,4‘-dicarboxylic acid) due to a lower absorbance in the red part of the visible spectrum. Density functional theory (DFT) molecular orbital calculations rationalize the electronic properties of these phosphonated complexes.
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