4,4′,5,5′-Tetracarboxy-2,2′-bipyridine Ru(II) Sensitizers for Dye-Sensitized Solar Cells ChouChun-Cheng HuFa-Chun WuKuan-Lin DuanTainan ChiYun LiuShih-Hung LeeGene-Hsiang ChouPi-Tai 2014 Two Ru­(II) sensitizers TCR-1 and TCR-2 bearing four carboxy anchoring groups were prepared using 4,4′,5,5′-tetraethoxycarbonyl-2,2′-bipyridine chelate and 4-(5-hexylthien-2-yl)-2-(3-trifluoromethyl-1<i>H</i>-pyrazol-5-yl)­pyridine and 6-<i>t</i>-butyl-1-(3-trifluoromethyl-1<i>H</i>-pyrazol-5-yl)­isoquinoline, respectively. Dissolution of these sensitizers in DMF solution afforded a light green solution up to 10<sup>–5</sup> M, for which their color gradually turned red upon further dilution and deposition on the surface of a TiO<sub>2</sub> photoanode due to the spontaneous deprotonation of carboxylic acid groups. These sensitizers were characterized using electrochemical means and structural analysis time-dependent density functional theory (TDDFT) simulation and were also subjected to actual device fabrication. The as-fabricated DSC devices showed overall efficiencies η = 6.16% and 6.23% versus their 4,4′-dicarboxy counterparts TFRS-2 and TFRS-52 with higher efficiencies of 7.57% and 8.09%, using electrolyte with 0.2 M LiI additive. Their inferior efficiencies are possibly caused by the combination of blue-shifted absorption on TiO<sub>2</sub>, inadequate dye loading, and the perpendicularly oriented central carboxy groups.