Multicolor electrochromic poly(amide-imide)s with N,N-diphenyl-N′,N′-di-4-tert-butylphenyl-1,4-phenylenediamine moieties

Abstract

A new imide ring-preformed dicarboxylic acid monomer bearing the N,N,N′,N′-tetraphenyl-1,4-phenylenediamine (TPPA) unit, i.e., N,N-bis(4-tert-butylphenyl)-N′,N′-bis(4-carboxyphthalimido)-1,4-phenylenediamine (2), was synthesized from the condensation of N,N-bis(4-aminophenyl)-N′,N′-bis(4-tert-butylphenyl)-1,4-phenylenediamine (1) and two equivalent amount of trimellitic anhydride (TMA). A new series of aromatic poly(amide-imide)s (PAIs) 4a–4g containing the electroactive TPPA moiety were prepared from the diimide-diacid 2 with various aromatic diamines by the phosphorylation polyamidation reaction. All the polymers were readily soluble in many organic solvents and could be solution-cast into tough and flexible polymer films. They displayed moderate to high glass-transition temperatures (280–320 °C) and good thermal stability. For the PAIs derived from common aromatic diamines, cyclic voltammograms of their cast films on the indium–tin oxide (ITO)-coated glass substrate exhibited two reversible oxidation redox couples around 0.68 and 1.10 V vs. Ag/AgCl in acetonitrile solution, and they revealed high redox and electrochromic stability with a color change from colorless neutral form to yellow and blue oxidized forms at applied potentials scanning from 0.0 to 1.3 V. Cyclic voltammograms of PAIs 4f and 4g obtained from diimide-diacid 2 and triphenylamine-based diamines exhibited three and four reversible oxidation redox couples, respectively. Because there are more than two redox states are electrochemically accessible from PAIs 4f and 4g, they could form tristable and even tetrastable color species and thus could display several colors upon oxidation at varying applied voltages. The electrochromic performance of a representative PAI 4c was investigated. This anodically coloring polymer film showed good electrochromic properties with high coloration efficiency (CE = 268 cm² C⁻¹ for the yellow coloration) and high optical contrast ratio of transmittance change (ΔT%) up to 33% at 411 nm and 32% at 922 nm for the yellow coloring, and 72% at 698 nm for the blue coloring. After over 100 cyclic switches, the polymer films still retained excellent redox and electrochromic activity.