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.

Ruthenium Complexes as Sensitizers in Dye-Sensitized Solar Cells

“…Depending on the substituents on both, cyclometalating and polypyridine, ligands one may choose from the above-mentioned procedures. To synthesize cyclometalated Ru complexes of [Ru(tpy)(dpb)] + type (where dpbH = 1,3bis(pyridine-2-yl)benzene) with two tridentate ligands, one may start from Ru(tpy)Cl3 and abstract halogens with soluble silver salts, i.e., AgPF6 or AgBF4, in acetone, and then, without specific purification, react the obtained acetone ligated complex with a cyclometalating ligand as shown in Scheme 3 [94,96,[100][101][102][103][104]. Direct reaction of Ru(tpy)Cl3 with cyclometalating ligand in the presence of base/reducing agent was also shown to provide cyclometalation [95,[105][106][107].…”