Multistate Electrochromic Covalent Organic Framework Film for Electronic Safety Indicator

The smart design of a conjugated organic framework with tunable redox functionalities could lead to multistate color switching under minimal operating voltage, which is desirable for low-energy-consuming optoelectronics. Herein, we have developed a two-dimensional electrochromic covalent organic framework (EC-COF) film exhibiting broad absorption across the ultraviolet–visible–near-infrared (NIR) range under applied potentials. The EC-COF films grown on an indium tin oxide-coated glass substrate show three-state anodic electrochromism with a high color contrast of ∼60% in the NIR region. The EC-COF film shows reversible color changes with high coloration efficiency and fast switching response (coloration time: 4.9 s; bleaching time: 10.6 s at 1100 nm). The highly porous nature of EC-COF facilitates ion movement through 1D pore channels. Demonstrating the real-time application of electrochemical attributes, we have developed, for the first time, a prototype device employing an EC-COF film as a safety indicator for electronic circuits. The device, coupled with a customized cellphone application, has been demonstrated for monitoring the safety of electronic sensor systems through subtle color variation under a range of potentials with a close-to-perfect accuracy of ∼98%. The current study provides a new avenue for the function-led development of multicolored electrochromic porous organic materials in advanced energy-efficient display devices.