A Series of Multicolor Electrochromic Ruthenium(II) Trisbipyridine Complexes:  Synthesis and Electrochemistry

A series of 5,5‘-disubstituted 2,2‘-bipyridines and their corresponding tris complexes with ruthenium(II) have been synthesized. The substituents used (ketone, ester, nitrile, imide, and two amides) are all electron withdrawing in nature and, with one exception, contain a carbonyl group in the position α to the bipyridine ring. The reduction potentials of the free ligands and ruthenium complexes have been determined by cyclic voltammetry and are correlated with the Hammett σ constants of the substituents. Finally, the electron-withdrawing nature of these substituents shifts the reduction potentials of each complex sufficiently positive that up to six stable ligand-based reductions are observable. In these reduced oxidation states, all of the complexes display multicolor electrochromism.