Nanometer-Thick Conjugated Microporous Polymer Films for Selective and Sensitive Vapor-Phase TNT Detection

Conjugated microporous polymer (CMP) thin films often show fast and amplified signal response and potential for developing portable sensing devices. Here, we elucidate electrochemical generation of three CMP thin films and their fluorescence response to trinitrotoluene (TNT). A tetra(carbazolylphenyl)ethylene monomer TPETCz-derived CMP thin film (PTPETCz, SBET: 930 m2/g) displayed fluorescence (λmax = 525 nm) quenching to nearly 95% in 3 min, when the CMP film is exposed to 33 ppb TNT vapors. Interestingly, PTPETCz is highly sensitive (30% quenching) to TNT vapors of low concentrations (5–10 ppb) and also remarkably selective toward TNT compared to other analytes. In contrast, an only mere response was observed when a nonporous monomer TPETCz-film was exposed to 0.2 ppm TNT. So, the microporosity and extended π-conjugation of the polymer facilitating suitable host–guest interactions is found to be essential toward highly sensitive detection of TNT. Fluorenone-cored CMP thin films (PFLCz) showed no response, while PTPEFLCz containing both tetraphenylethylene and fluorenone structural units showed nearly 70% of emission quenching in the presence of 0.2 ppm TNT. Therefore, the presence of electron-donating TPE core is a prerequisite for efficient photoinduced electron transfer from polymer to nitroarenes.