A visible light/heat responsive covalent organic framework for highly efficient and switchable proton conductivity.

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Covalent organic frameworks (COFs) show promise for proton-exchange membranes, chemical sensors, and electronic devices.
• Designing COFs with high proton conductivity and stimulus-responsive properties presents a significant challenge.

Purpose of the Study:

• To synthesize and characterize the first light/heat switchable COF.
• To investigate the proton conductivity and switching performance of the novel COF.

Main Methods:

• Grafting donor-acceptor Stenhouse adduct (DASA) units into a β-ketoenamine-based COF.
• Investigating reversible photoisomerization of DASA groups using visible light and heat.
• Measuring proton conductivity under varying conditions and cycling stability.
• Utilizing DFT calculations to rationalize experimental findings.
• Demonstrating a proof-of-concept optical control device.

Main Results:

• Synthesized COF-HNU9, a light/heat switchable COF with DASA groups in its channels.
• Observed reversible open-closed photoisomerization of DASA upon visible light irradiation and thermal recovery.
• Achieved a three-order-of-magnitude increase in proton conductivity under visible light at 98% RH.
• Demonstrated high proton conductivity of up to 0.02 S cm⁻¹ at 80 °C with excellent cycling stability (>20 cycles).
• Verified a Grotthuss-type mechanism for proton conduction via DFT calculations.

Conclusions:

• COF-HNU9 represents a significant advancement in stimuli-responsive COFs.
• The material offers high proton conductivity and effective light/heat switching capabilities.
• Demonstrated potential for applications in optical control devices and remote-controlled electronics.