Polyimide-polyether mixed conductors as switchable materials for electrochromic devices

Abstract

A new family of redox-active polymers have been obtained by polycondensation of α,ω-diamino oligopolyethers with various aromatic tetracarboxylic acid anhydrides. The polyether blocks retain the usual cation co-ordination ability leading to solid-state ionic conduction while the relatively large electron affinity of the bis-imide moieties formed in the block polymers allows the reversible formation of stable radical anions (• − and •• 2−) in the range 2–2.6 V vs. Li°. Either slow-scan or microelectrode voltammetry indicate that the totality of the redox centres in such materials are readily accessible for all polyether spacer lengths tested (6–22 ether fragments), suggesting both a fast electron-exchange mechanism between anion radicals and a tendency for self assembly (stacking) of the planar aromatic groups. When increasing the number of atoms in the aromatic ring, the peak separation became smaller (benzene > naphthalene > perylene), resulting ultimately in simultaneous 2-electrons injection. These materials, due to the high coloration efficiency of the reduced state and their ready processability in thin films are excellent candidate for the realisation of laminated solid-state electrochromic devices.