Multifunctional Two-Dimensional Tetrazine-Based Polymerfor an Inverse Electron Demand Diels–Alder Reaction and Room-TemperatureNO₂ Sensing

A multifunctional tetrazine-integrated π-conjugated two-dimensional (2D) porous organic polymer (CMP) (<b>PTz</b>) has been developed by the self-condensation of benzene-1,3,5-tricarbonitrile in the presence of sulfur and hydrazine hydrate via the Pinner synthetic strategy. <b>PTz</b> has been further postmodified into a pyridazine polymer (<b>PPz</b>) through an inverse electron demand Diels–Alder (IEDDA) reaction using ethyl vinyl ether, which allows the tuning of structural, optical, and electronic properties. DFT revealed a 0.6 eV difference in band gap between the two polymers, with <b>PTz</b> having a narrow band gap of 1.6 eV and <b>PPz</b> having a band gap of 2.2 eV. Furthermore, <b>PTz</b> is a red solid with an absorption red edge at 620 nm, whereas <b>PPz</b> produces a yellow solid with a blue-shifted absorption red edge of 480 nm. 2D <b>PTz</b> was utilized to form a resistive sensor for detecting NO₂, a prominent environmental pollutant. <b>PTz</b> exhibited an excellent sensitivity toward NO₂, with its response varying from −8.4 to −34.2% for 2–10 ppm of NO₂ at room temperature. The detection limit of <b>PTz</b> was found to be 337 ppb, and the response time and recovery time ranged from 176 to 273 s and 307 to 443 s, respectively, for a concentration range of 2 to 10 ppm of NO₂. The polymer exhibited high selectivity toward NO₂ among different tested analytes (CO, SF₆, NH₃, H₂O, and H₂S).