Two-Dimensional Chemiresistive Covalent Organic Framework with High Intrinsic Conductivity

Area of Science:

• Materials Science
• Nanotechnology
• Chemistry

Background:

• Two-dimensional (2D) materials offer unique electronic properties.
• Covalent Organic Frameworks (COFs) are crystalline porous polymers with tunable structures.
• Developing intrinsically conductive COFs is crucial for advanced electronic applications.

Purpose of the Study:

• To synthesize a novel intrinsically conductive 2D COF.
• To investigate the gas-sensing properties of the synthesized COF.
• To elucidate the mechanism behind the COF's gas-sensing response.

Main Methods:

• Aromatic annulation reaction between nickel(II) octa-aminophthalocyanine and pyrene-4,5,9,10-tetraone.
• Electrical conductivity measurements before and after iodine (I2) doping.
• Fabrication of chemiresistive devices for gas sensing.
• Electronic structure calculations.
• Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analyses.

Main Results:

• A novel intrinsically conductive 2D COF, COF-DC-8, was successfully synthesized.
• The COF-DC-8 exhibited an intrinsic bulk conductivity of 2.51 × 10⁻³ S/m, increasing by three orders of magnitude upon I2 doping.
• The material demonstrated high sensitivity and selectivity for detecting various gases (NH3, H2S, NO, NO2) at parts-per-billion (ppb) levels.
• Electronic calculations indicated an anisotropic band structure potentially contributing to conductivity.
• Studies suggested charge transfer interactions between analytes and the nickelphthalocyanine component are responsible for the sensing mechanism.

Conclusions:

• The synthesized COF-DC-8 is a promising intrinsically conductive material for gas sensing applications.
• The material's conductivity and gas-sensing performance can be significantly enhanced through doping.
• The nickelphthalocyanine unit plays a key role in the charge transfer mechanism for gas detection.