Macrocycle-Based Metal-Organic Frameworks with NO₂-Driven On/Off Switch of Conductivity

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Conductive metal-organic frameworks (MOFs) are crucial for energy applications like supercapacitors and fuel cells.
• The development of gas-driven conductive MOFs, which can dynamically alter conductivity in response to gas, remains an unexplored area.

Purpose of the Study:

• To synthesize and characterize a novel gas-driven conductive MOF.
• To investigate the mechanism of conductivity modulation by gas adsorption.
• To demonstrate the potential of this MOF as a switchable conductive material.

Main Methods:

• Synthesis of a macrocycle-based MOF (A) using calix[4]resorcinarene and Co(II) cations.
• Measurement of electrical conductivity of MOF A before and after NO2 adsorption.
• Analysis of the crystal structure of the NO2-adsorbed MOF (A-NO2) to elucidate the conductive pathways.

Main Results:

• MOF A demonstrated a significant conductivity enhancement of approximately eight orders of magnitude upon NO2 adsorption, increasing from 1.3 × 10^-11 S/cm to 8.4 × 10^-4 S/cm.
• The MOF exhibited a reversible insulator-to-conductor transition, returning to an insulating state within 42 seconds upon NO2 evacuation.
• Crystal structure analysis revealed that adsorbed NO2 molecules facilitate conductive pathways through hydrogen bonding, connecting metal clusters and reducing electron transmission distances.

Conclusions:

• A novel macrocycle-based MOF (A) has been successfully synthesized, exhibiting gas-driven conductivity switching triggered by NO2.
• The reversible on/off conductivity switch, driven by NO2 adsorption and desorption, highlights the potential for designing advanced gas-responsive conductive materials.
• This work opens new avenues for developing smart MOF-based systems for gas detection and modulation applications.