Three‐Dimensional Covalent Organic Framework Film for Fast and Ultrastable Near‐Infrared Electrochromism

Abstract

Electrochromic (EC) covalent organic framework (COF) films provide ordered porous platforms for coupling redox‐active skeletons with ion transport, yet their long‐term operation is often limited by inefficient counterion compensation, sluggish electron transport, and redox‐induced structural instability. Herein, we report a metal‐free three‐dimensional (3D) COF film for fast and ultrastable near‐infrared (NIR) electrochromism. The 3D‐COFTPDA‐TFPB film integrates bis(triphenylamine)‐derived TPDA redox centers into a crystalline fmj‐type framework with interconnected micro/mesoporous channels. This 3D architecture promotes electrolyte penetration and counterion‐coupled charge compensation, while the imine‐linked conjugated skeleton enhances charge delocalization and stabilizes oxidized states. Consequently, the optimized film delivers a large optical contrast of 73% at 1020 nm, rapid coloration/bleaching time of 0.54/0.27 s, a high coloration efficiency of 648.3 cm2 C−1, and an open‐circuit optical memory of 4.6 h. Notably, it retains 97.6% of its maximum optical modulation after 10,300 switching cycles, demonstrating outstanding cycling durability among COF‐based EC films. In situ Raman, X‐ray photoelectron spectroscopy and theoretical calculations reveal that the EC response originates from reversible TPDA‐centered polaron/bipolaron evolution stabilized within the 3D framework. A quasi‐solid‐state device further preserves distinct optical modulation. This work establishes 3D COF films as a promising platform for fast, efficient, and durable electrochromism.