Conducting redox polymers: investigations of polythiophene-Ru(bpy)3n+ hybrid materials

Abstract

A series of thiophene-appended Ru ^II (bpy) ₃ derivatives, Ru(1) ₃ , Ru(2) ₃ , Ru(3) ₃ , Ru(bpy) ₂ (1), and Ru(bpy) ₂ (2), and their resulting polymers have been synthesized and characterized. The bpy ligands 5,5′-bis(5-(2,2′-bithienyl))-2,2′-bipyridine, 1, 4,4′-bis(5-(2,2′-bithienyl))-2,2′-bipyridine, 2, and 4-(5-(2,2′-bithienyl))-2,2′-bipyridine, 3, all contain electrochemically polymerizable bithienyl moieties. The monomers Ru(2) ₃ , Ru(3) ₃ , Ru(bpy) ₂ (1) and Ru(bpy) ₂ (2) display spectroscopic features that are similar to the ligand-based and MLCT bands found for Ru(bpy) ₃ . The cyclic voltammograms of all of these polymers display both metal-centered and thiophene-based electroactivity. High redox conductivity was found in poly(Ru(2) ₃ ) and poly(Ru(3) ₃ ) for both the thiophene-based oxidation and metal-based reduction processes. These results indicate that the polymers display charge localization for both the metal complexes as well as the tetrathienyl connecting units. The degree of interconnection (number of linkages) as well as the substitution pattern were found to control the conductivity of these polymers. The highest conductivity (3.3×10 ^–3 S cm ^–1 ) was found for poly(Ru(2) ₃ ), which is able to have up to 6 linkages with other ruthenium complexes as well as possessing a 4,4′-substitution pattern that allows effective orbital overlap of the conjugated polymer backbone with the ruthenium centers.