Semiconducting Cu(I) Framework for Room Temperature NO₂ Sensing via Efficient Charge Transfer

Efficient room-temperature sensors for toxic gases are essential to ensure a safe and healthy life. Conducting frameworks have shown great promise in advancing gas sensing technologies. In this study, two new organic-inorganic frameworks [Cu₂X₂(PPh₃)₂(L)]_n, CP1 (X = I) and CP2 (X = Br) have been synthesized using (pyridin-4-yl)-N-(4H-1,2,4-triazol-4-yl)methanimine (L) and triphenylphosphine. These frameworks exhibit distinct structural arrangements to generate 1D coordination polymers (CPs). Due to their semiconducting properties, both CPs are fabricated into conventional interdigitated electrodes by drop-casting. Benefitting from the higher electron density of the Cu(I) center, CP1 demonstrates selective sensing for NO₂ gas with excellent sensitivity and reversibility. The material offers one of the best room temperature NO₂ chemiresistive sensing performances among the MOF/CP-based materials with ultrafast response time (15.5 s @10 ppm). Additionally, convenient synthesis and ease of device fabrication for sensing give the material a distinct advantage. The experimental and theoretical findings collectively suggest that the adsorption of NO₂ on the material's surface and the concomitant effective charge transfer between Cu(I) and NO₂ are key to its efficacious gas sensing capabilities.