This paper describes the first demonstration of using a series of isoreticular nickel phthalocyanine- and nickel naphthalocyanine-based bimetallic conductive two-dimensional (2D) metal–organic frameworks (MOFs) as active materials in chemiresistive sensing of gases. Devices achieve exceptional sensitivity at sub-part-per-million (ppm) to part-per-billion (ppb) detection limits toward NH3 (0.31–0.33 ppm), H2S (19–32 ppb), and NO (1.0–1.1 ppb) at low driving voltages (0.01–1.0 V) within 1.5 min of exposure. The devices maintain their performance in the presence of humidity (5000 ppm of H2O). The isoreticular analogs enable modular control over selectivity and sensitivity in gas sensing through different combinations of linkers and metal nodes. Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy studies suggest that the chemiresistive response of the MOFs involves charge transfer interactions triggered by the analytes adsorbed on MOFs.

This paper describes the first demonstration of a general concept for achieving facile proton conduction within a class of layered two-dimensional aza-fused π-conjugated covalent organic frameworks (COFs). The built-in phenanthroline moieties promote efficient adsorption of water and acidification by H3PO4 to produce excellent proton conductivities of 10–5 and 10–3 S/cm for the pristine and acidified analogues, respectively. These molecular design concepts are poised for development of highly stable proton-conducting materials.

The synthetically tunable properties and intrinsic porosity of conductive metal-organic frameworks (MOFs) make them promising materials for transducing selective interactions with gaseous analytes in an electrically addressable platform. Consequently, conductive MOFs are valuable functional materials with high potential utility in chemical detection. The implementation of these materials, however, is limited by the available methods for device incorporation due to their poor solubility and moderate electrical conductivity. This manuscript describes a straightforward method for the integration of moderately conductive MOFs into chemiresistive sensors by mechanical abrasion. To improve electrical contacts, blends of MOFs with graphite were generated using a solvent-free ball-milling procedure. While most bulk powders of pure conductive MOFs were difficult to integrate into devices directly via mechanical abrasion, the compressed solid-state MOF/graphite blends were easily abraded onto the surface of paper substrates equipped with gold electrodes to generate functional sensors. This method was used to prepare an array of chemiresistors, from four conductive MOFs, capable of detecting and differentiating NH3, H2S and NO at parts-per-million concentrations.

The recent development of metallophthalocyanine (MPc)-based frameworks has opened the door to a new class of promising multifunctional materials with emergent electrical, magnetic, optical, and electrochemical properties. This perspective article outlines the process of molecular engineeringwhich uses the strategic selection and combination of molecular components to guide the assembly of materials and achieve target functionto demonstrate how the choice of MPc-based molecular components combined with the toolkit of reticular chemistry leads to the emergence of structure−property relationships in this class of materials. The role of complexity and emergence as core principles of molecular engineering of functional materials is discussed. Subsequent illustration of the molecular design criteria that stem from the unique optical, electrical, magnetic, and electrochemical features of MPc monomers sets the stage for achieving emergent function on the basis of the underlying properties of the constituent molecular building blocks. The review of strategies available for the controlled assembly of MPc monomers employing the principles of self-assembly and reticular chemistry serves as a guide for the attainment of enhanced control over relative position, orientation, and aggregation of MPc building blocks, while creating opportunities to discover new emergent properties. The central focus on the advances in MPc-based framework materials shows how the electronic, photophysical, magnetic, and electrochemical properties in these materials emerge from molecular design principles that build on the initial properties embedded in MPc-based building blocks. Concluding remarks summarize accomplishments and pave the way for future directions.

This paper describes the demonstration of aseries of heterobimetallic,i soreticular 2D conductive metal-organic frameworks (MOFs) with metallophthalocyanine (MPc,M= Co and Ni)u nits interconnected by Cu nodes towards lowpower chemiresistive sensing of ppm levels of carbon monoxide (CO). Devices achieve as ub-part-per-million (ppm) limit of detection (LOD) of 0.53 ppm toward CO at al ow driving voltage of 0.1 V. MPc-based Cu-linked MOFs can continuously detect CO at 50 ppm, the permissible exposure limit required by the Occupational Safety and Health Administration (OSHA), for multiple exposures,a nd realizeC O detection in air and in humid environment. Diffuse reflectance infrared Fourier transform spectroscopy( DRIFTS), density functional theory (DFT) calculations,and comparison experiments suggest the contribution of Cu nodes to CO binding and the essential role of MPc units in tuning and amplifying the sensing response.

This paper describes the design, synthesis, characterization, and performance of a novel semiconductive crystalline coordination network, synthesized using 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) ligands interconnected with bismuth ions, toward chemiresistive gas sensing. Bi(HHTP) exhibits two distinct structures upon hydration and dehydration of the pores within the network, Bi(HHTP)-α and Bi(HHTP)-β, respectively, both with unprecedented network topology (2,3-c and 3,4,4,5-c nodal net stoichiometry, respectively) and unique corrugated coordination geometries of HHTP molecules held together by bismuth ions, as revealed by a crystal structure resolved via microelectron diffraction (MicroED) (1.00 Å resolution). Good electrical conductivity (5.3 × 10 –3 S·cm –1 ) promotes the utility of this material in the chemical sensing of gases (NH 3 and NO) and volatile organic compounds (VOCs: acetone, ethanol, methanol, and isopropanol). The chemiresistive sensing of NO and NH 3 using Bi(HHTP) exhibits limits of detection 0.15 and 0.29 parts per million (ppm), respectively, at low driving voltages (0.1–1.0 V) and operation at room temperature. This material is also capable of exhibiting unique and distinct responses to VOCs at ppm concentrations. Spectroscopic assessment via X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopic methods (i.e., attenuated total reflectance-infrared spectroscopy (ATR-IR) and diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS)), suggests that the sensing mechanisms of Bi(HHTP) to VOCs, NO, and NH 3 comprise a complex combination of steric, electronic, and protic properties of the targeted analytes.

This paper describes the demonstration of a series of heterobimetallic, isoreticular 2D conductive metal–organic frameworks (MOFs) with metallophthalocyanine (MPc, M=Co and Ni) units interconnected by Cu nodes towards low‐power chemiresistive sensing of ppm levels of carbon monoxide (CO). Devices achieve a sub‐part‐per‐million (ppm) limit of detection (LOD) of 0.53 ppm toward CO at a low driving voltage of 0.1 V. MPc‐based Cu‐linked MOFs can continuously detect CO at 50 ppm, the permissible exposure limit required by the Occupational Safety and Health Administration (OSHA), for multiple exposures, and realize CO detection in air and in humid environment. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), density functional theory (DFT) calculations, and comparison experiments suggest the contribution of Cu nodes to CO binding and the essential role of MPc units in tuning and amplifying the sensing response.

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