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

Abstract

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. 1 a, 2 a, and 3 a, with donating and accepting ligands. Complexes 2 a and 3 a are coordinated with 2,6-di(quinolin-8-yl)-4-methoxycarbonylpyridine (dqpCO2Me), and 1 a with 2,2’:6’,2’’-terpyridine-4’-ethoxycarbonyl (tpyCO2Et) accepting ligands. Interestingly, the binding mode of the accepting ligand was found to differ in 3 a and 2 a. NMR spectra and single crystal XRD data reveal that in 3 a one of the quinolines of dqpCO2Me ligand is cyclometalated, while in 2 a the ligand coordinates in an expected fashion similar to tpyCO2Et. The ester groups in 1 a and 2 a 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 1H, 13C and 1H-1H COSY NMR, and high-resolution mass analyses of all complexes were conducted.