4,4′-Unsymmetrically substituted-2,2′-bipyridines: novel bidentate ligands on ruthenium(ii) [3+2+1] mixed ligand complexes for efficient sensitization of nanocrystalline TiO2 in dye solar cells

A series of five new ruthenium [3 + 2 + 1] complexes coded as MC107-MC111, with novel unsymmetrical bipyridines as ancillary ligands and terpyridine tricarboxylic acid as an anchoring ligand have been successfully synthesized and characterized by H-1 NMR, C-13 NMR and UV-Visible spectrometry. Improvement in the molar extinction coefficient of all these sensitizers was observed compared with reference standard N749 dye under comparable conditions. Among all the new sensitizers MC108 exhibited a maximum solar to electrical conversion efficiency of 5.573% (J(sc) 16.81 mA cm(-2), V-oc = 0.50 V. FF = 0.65) under standard global AM 1.5 G solar condition, when compared to the N749 dye with an efficiency of 6.29% (J(sc) = 13.74 mA cm(-2), V-oc = 0.67 V. FF = 0.68) under similar fabrication and evaluation conditions. Density functional theory (DFT) and time-dependent DFT calculations are carried out for MC107-MC111 to understand their structural, electronic and photophysical properties.