High-performance transmissive-to-black electrochromism derived from diphenylamine-based polyimides with tetraphenylethylene as bridging units

Abstract

Transmissive-to-black switching electrochromic (EC) polymers have attracted considerable attention toward the development of low-cost, low-energy-demand passive displays. However, most reported transmissive-to-black switching EC polymers have high applied potential and low cycling stability, which significantly restrict their practical application. To address this issue, we propose a new structure design concept from the perspective of molecular structural changes by systematically investigating three different types of tetraphenylethylene (TPE)-based π-bridges connected with a diphenylamine (DPA) electroactive unit (pendant-grouped, straight-chained, and hyperbranched). The structural changes of the TPE-based π-bridge during electrochemical redox and the EC performance of polyimides are studied. All the designed polyimides (PG-TPE-PI, ST-TPE-PI, and HB-TPE-PI) exhibit overall transmissive-to-black EC performance. In particular, PG-TPE-PI presents a high response speed (2.29 s/2.51 s), excellent open circuit stability (over 24 h/72 h), and high coloration efficiency (566 cm² C⁻¹), as well as first-class cycling stability for a transmissive-to-black polymer material (3000 cycles in an open system), thereby showing excellent application potential.