Redox-bipolar mesoporous two-dimensional covalent organic framework for multi-color electrochromism.

Area of Science:

• Materials Science
• Nanotechnology
• Electrochemistry

Background:

• Two-dimensional covalent organic frameworks (COFs) show promise for electrochromic devices.
• Current COFs often suffer from inefficient ion transport and limited performance due to microporosity and monopolar structures.

Purpose of the Study:

• To design and synthesize a novel mesoporous, hexagonal bipolar COF with a donor-acceptor heterostructure.
• To investigate the electrochromic properties and device performance of the new COF material.

Main Methods:

• Synthesis of a bipolar COF using triphenylamine (donor) and naphthalene dianhydride (acceptor) units.
• Fabrication of symmetric electrochromic devices utilizing the synthesized COF.
• Characterization of electrochromic performance, including optical contrast, spectral tunability, and cycling stability.

Main Results:

• The bipolar COF exhibits efficient bidirectional ion transport and intramolecular charge transfer.
• Multicolor electrochromism with distinct transitions (brown-pale-blue-green) was observed.
• High optical contrasts (e.g., 80% at 850 nm) and excellent stability (>91% retention after 500 cycles) were achieved.
• Symmetric devices demonstrated broad spectral tunability (400-1100 nm) and outstanding cycling stability (<1.5% decay after 1000 cycles).

Conclusions:

• The developed mesoporous bipolar COF establishes a new benchmark for COF-based electrochromic systems.
• The D-A heterostructure design facilitates superior ion utilization and electron transport for enhanced electrochromic performance.
• This work opens avenues for next-generation electrochromic materials with improved color switching and durability.