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Sensing complex gaseous mixtures and identifying their composition and concentration have the potential to achieve unprecedented improvements in environmental monitoring, medical diagnostics, industrial safety, and the food/agriculture industry. Electronically transduced chemical sensors capable of recognizing and differentiating specific target gases and transducing these chemical stimuli in a portable electronic device offer an opportunity for impact by bridging the utility of chemical information with global wireless connectivity. Among electronically transduced chemical sensors, chemiresistors stand out as particularly promising due to combined features of low-power requirements, room temperature operation, non-line-of-sight detection, high portability, and exceptional modularity. Relying on changes in resistance of a functional material triggered by variations in the surrounding chemical environment, these devices have achieved part-per-billion sensitivities of analytes by employing conductive polymers, graphene, carbon nanotubes (CNTs), metal oxides, metal nanoparticles, metal dichalcogenides, or MXenes as sensing materials. Despite these tremendous developments, the need for stable, selective, and sensitive chemiresistors demands continued innovation in material design in order to operate in complex mixtures with interferents as well as variations in humidity and temperature. To fill existing gaps in sensing capabilities, conductive metal−organic frameworks (MOFs) and covalent organic frameworks (COFs) have recently emerged as a promising class of materials for chemiresistive sensing. In contrast to previously reported chemiresistors, these materials offer at least three unique features for gas sensing applications: (i) bottom-up synthesis from molecularly precise precursors that allows for strategic control of material−analyte interactions, (ii) intrinsic conductivity that simultaneously facilitates charge transport and signal transduction under low power requirements, and (iii) high surface area that enables the accessibility of abundant active sites and decontamination of gas streams by coordinating to and, sometimes, detoxifying harmful analytes. Through an emphasis on molecular engineering of structure−property relationships in conductive MOFs and COFs, combined with strategic innovations in device integration strategies and device form factor (i.e., the physical dimensions and design of device components), our group has paved the way to demonstrating the multifunctional utility of these materials in the chemiresistive detection of gases and vapors. Backed by spectroscopic assessment of material−analyte interactions, we illustrated how molecular-level features lead to device performance in detection, filtration, and detoxification of gaseous analytes. By merging the bottom-up synthesis of these materials with device integration, we show the versatility and scalability of using these materials in low-power electronic sensing devices. Taken together, our achievements, combined with the progress spearheaded on this class of materials by other researchers, establish conductive MOFs and COFs as promising multifunctional materials for applications in electronically transduced, portable, low-power sensing devices. 

Abstract This paper describes the use of a highly crystalline conductive 2D copper₃(hexaiminobenzene)₂(Cu₃(HIB)₂) as an ultrasensitive (limit of detection of 1.8 part‐per‐billion), highly selective, reversible, and low power chemiresistive sensor for nitric oxide (NO) at room temperature. The Cu₃(HIB)₂‐based sensors retain their sensing performance in the presence of humidity, and exhibit strong signal enhancement towards NO over other highly toxic reactive gases, such as NO₂, H₂S, SO₂, NH₃, CO, as well as CO₂. Mechanistic investigations of the Cu₃(HIB)₂‐NO interaction through spectroscopic analyses and density functional theory revealed that the Cu‐bis(iminobenzosemiquinoid) moieties serve as the binding sites for NO sensing, while the Ni‐bis(iminobenzosemiquinoid) MOF analog shows no noticeable response to NO. Overall, these findings provide a significant advance in the development of crystalline metal‐bis(iminobenzosemiquinoid)‐based conductive 2D MOFs as highly sensitive, selective, and reversible sensing materials for the low‐power detection of toxic gases.