Electrically−transduced sensors, with their simplicity and compatibility with standard electronic technologies, produce signals that can be efficiently acquired, processed, stored, and analyzed. Two dimensional (2D) nanomaterials, including graphene, phosphorene (BP), transition metal dichalcogenides (TMDCs), and others, have proven to be attractive for the fabrication of high−performance electricallytransduced chemical sensors due to their remarkable electronic and physical properties originating from their 2D structure. This review highlights the advances in electricallytransduced chemical sensing that rely on 2D materials. The structural components of such sensors are described, and the underlying operating principles for different types of architectures are discussed. The structural features, electronic properties, and surface chemistry of 2D nanostructures that dictate their sensing performance are reviewed. Key advances in the application of 2D materials, from both a historical and analytical perspective, are summarized for four different groups of analytes: gases, volatile compounds, ions, and biomolecules. The sensing performance is discussed in the context of the molecular design, structure−property relationships, and device fabrication technology. The outlook of challenges and opportunities for 2D nanomaterials for the future development of electrically-transduced sensors is also presented.

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.

This paper describes the first implementation of an array of two-dimensional (2D) layered conductive metal−organic frameworks (MOFs) as drop-casted film electrodes that facilitate voltammetric detection of redox active neurochemicals in a multianalyte solution. The device configuration comprises a glassy carbon electrode modified with a film of conductive MOF (M 3 HXTP

This paper describes the identification of specific host−guest interactions between basic gases (NH 3 , CD 3 CN, and pyridine) and four topologically similar 2-dimensional (2D) metal− organic frameworks (MOFs) comprising copper and nickel bis(diimine) and bis(dioxolene) linkages of triphenylene-based ligands using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and powder X-ray diffraction (PXRD). This contribution demonstrates that synthetic bottom-up control over surface chemistry of layered MOFs can be used to impart Lewis acidity or a mixture of Brønsted and Lewis acidities, through the choice of organic ligand and metal cation. This work also distinguishes differences in redox activity within this class of MOFs that contribute to their ability to promote electronic transduction of intermolecular interactions. Future design of structure−function relationships within multifunctional 2D MOFs will benefit from the insights this work provides.

This paper describes a novel synthetic approach for the conversion of zero-valent copper metal into a conductive two-dimensional layered metal–organic framework (MOF) based on 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) to form Cu3(HHTP)2. This process enables patterning of Cu3(HHTP)2 onto a variety of flexible and porous woven (cotton, silk, nylon, nylon/cotton blend, and polyester) and non-woven (weighing paper and filter paper) substrates with microscale spatial resolution. The method produces conductive textiles with sheet resistances of 0.1–10.1 MΩ/cm2, depending on the substrate, and uniform conformal coatings of MOFs on textile swatches with strong interfacial contact capable of withstanding chemical and physical stresses, such as detergent washes and abrasion. These conductive textiles enable simultaneous detection and detoxification of nitric oxide and hydrogen sulfide, achieving part per million limits of detection in dry and humid conditions. The Cu3(HHTP)2 MOF also demonstrated filtration capabilities of H2S, with uptake capacity up to 4.6 mol/kgMOF. X-ray photoelectron spectroscopy and diffuse reflectance infrared spectroscopy show that the detection of NO and H2S with Cu3(HHTP)2 is accompanied by the transformation of these species to less toxic forms, such as nitrite and/or nitrate and copper sulfide and S x species, respectively. These results pave the way for using conductive MOFs to construct extremely robust electronic textiles with multifunctional performance characteristics.

A combination of experimental and computational methods has been used to understand the reactivity and selectivity of orthogonal thiol-ene and thiol-yne ″click″ reactions involving N-allyl maleimide (1) and N-propargyl maleimide (2). Representative thiols methyl-3-mercaptopropionate and β-mercaptoethanol are shown to add exclusively and quantitatively to the electron poor maleimide alkene of 1 and 2 under base (Et3N) initiated thiol-Michael conditions. Subsequent radical-mediated thiol-ene or thiol-yne reactions can be carried out to further functionalize the remaining allyl or propargyl moieties in near quantitative yields (>95%). Selectivity, however, can only be achieved when base-initiated thiol-Michael reactions are carried out first, as radical-mediated reactions between equimolar amounts of thiol and N-substituted maleimides give complex mixtures of products. CBS-QB3 calculations have been used to investigate the energetics and kinetics of reactions between a representative thiol (methyl mercaptan) with N-allyl and N-propargyl maleimide under both base-initiated and radical-mediated conditions. Calculations help elucidate the factors that underlie the selective base-initiated and nonselective radical-mediated thiol-ene/yne reactions. The results provide additional insights into how to design selective radical-mediated thiol-ene/yne reactions.

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.