Design and synthesis of new Ru-complexes as potential photo-sensitizers: experimental and TD-DFT insights

Abstract

We report density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations on a novel organic ligand and a novel class of ruthenium complexes; cis-RuL₂X₂ with L = 2,2′-bipyridine-6,6′-bis ethyl ester phosphonate and phosphonic acid, X = Cl, CN or NCS. The calculations show that cis-configurations are more stable than the trans-counterparts. The DFT results have been used to help design such novel complexes for potential use as sensitizers. We demonstrate the opportunity to synthesize such complexes with high purity. The synthesis of these complexes relies on the preparation of the key intermediates cis-Ru(2,2′-bipyridine-6,6′-bisdiethyl ester phosphonate)Cl₂. These complexes were characterized by ¹H, ¹³C, and ³¹P NMR, elemental analysis and FTIR spectroscopy. The NCS complex shows the smallest optical band gap followed by the Cl and CN complexes, respectively, with the highest performance upon use as a sensitizer in dye-sensitized solar cells.