Electrochemical properties of non-conjugated electrochromic polymers derived from aromatic amine derivatives

The electrochemical and optical properties of two types of non-conjugated electrochromic polymers derived from aromatic amine derivatives (DDP-A, DDB-P) are presented. DDP-A is synthesized by the polymerization of N,N′-dimethyl-N,N′-diphenyl-1,4-phenylenediamine (DDP) and acetaldehyde (A), and DDB-P is polymerized with N,N′-dimethyl-N,N′-diphenylbenzidine (DDB) and propionaldehyde (P). Both DDP-A and DDB-P have a band gap in the ultraviolet region, and are colorless and transparent in neutral states. At one-electron oxidation states, DDP-A^{· +} absorbs light mainly in a visible region, whereas DDB-P^{· +} absorbs light mainly in a near-infrared (NIR) region. DDP-A^{· +} and DDB-P^{· +} are nitrogen-centered π-bridged mixed-valence compounds showing intervalence-charge transfer bands. The electrochemical and optical properties of DDP-A and DDB-P depend on the nitrogen-nitrogen distance correlating the electronic coupling of nitrogen redox centers. From the standpoint of energy saving, DDB-P is very interesting because it absorbs light in an NIR region. Finally, focusing on the smart window application, the optical properties of the solid-state electrochromic cell fabricated with DDP-A and heptyl viologen are examined. The cell was confirmed to be colored blue by applying a potential of about 1.0 V, and bleached at 0 V.