Two-Dimensional Chemiresistive Covalent Organic Framework with High Intrinsic Conductivity

This paper describes the synthesis of a novel intrinsically conductive two-dimensional (2D) covalent organic framework (COF) through the aromatic annulation of 2,3,9,10,16,17,23,24-octa-aminophthalocyanine nickel(II) and pyrene-4,5,9,10-tetraone. The intrinsic bulk conductivity of the COF material (termed COF-DC-8) reached 2.51 × 10^-3 S/m, and increased by 3 orders of magnitude with I₂ doping. Electronic calculations revealed an anisotropic band structure, with the possibility for significant contribution from out-of-plane charge-transport to the intrinsic bulk conductivity. Upon integration into chemiresistive devices, this conductive COF showed excellent responses to various reducing and oxidizing gases, including NH₃, H₂S, NO, and NO₂, with parts-per-billion (ppb) limits of detection (for NH₃ = 70 ppb, for H₂S = 204 ppb, for NO = 5 ppb, and for NO₂ = 16 ppb based on 1.5 min exposure). Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy studies suggested that the chemiresistive response of the COF-DC-8 involves charge transfer interactions between the analyte and nickelphthalocyanine component of the framework.