Bis-Tridentate-Cyclometalated Ruthenium Complexes with Extended Anchoring Ligand and Their Performance in Dye-Sensitized Solar Cells

Ruthenium polypyridine complexes with six-membered chelating rings have recently received significant attention due to their broad absorption spectra and outstanding photophysical characteristics. In this work we present the synthesis and characterization of three new heteroleptic bis-tridentate cyclometalated ruthenium complexes, i.e. 1a, 2a, and 3a, with donating and accepting ligands. Complexes 2a and 3a are coordinated with 2,6-di(quinolin-8-yl)-4-methoxycarbonylpyridine (dqpCO(2)Me), and 1a with 2,2':6',2 ''-terpyridine-4'-ethoxycarbonyl (tpyCO(2)Et) accepting ligands. Interestingly, the binding mode of the accepting ligand was found to differ in 3a and 2a. NMR spectra and single crystal XRD data reveal that in 3a one of the quinolines of dqpCO(2)Me ligand is cyclometalated, while in 2a the ligand coordinates in an expected fashion similar to tpyCO(2)Et. The ester groups in 1a and 2a were hydrolyzed to obtain sensitizers 1 and 2, which were used in dye-sensitized solar cells (DSCs) and the device performance with both iodine and cobalt-based electrolytes was investigated. Complete H-1, C-13 and H-1-H-1 COSYNMR, and high-resolution mass analyses of all complexes were conducted.