Electrogenerated Thin Films of Microporous Polymer Networks with Remarkably Increased Electrochemical Response to Nitroaromatic Analytes

Thin films of microporous polymer networks (MPNs) have been generated by electrochemical polymerization of a series of multifunctional carbazole-based monomers. The microporous films show high Brunauer–Emmett–Teller (BET) surface areas up to 1300 m² g^–1 as directly measured by krypton sorption experiments. A correlation between the number of polymerizable carbazole units of the monomer and the resulting surface area is observed. Electrochemical sensing experiments with 1,3,5-trinitrobenzene as prototypical nitroaromatic analyte demonstrate an up to 180 times increased current response of MPN-modified glassy carbon electrodes in relation to the nonmodified electrode. The phenomenon probably involves intermolecular interactions between the electron-poor nitroaromatic analytes and the electron-rich, high surface area microporous deposits, with the electrochemical reduction at the MPN-modified electrodes being an adsorption-controlled process for low scan rates. We expect a high application potential of such MPN-modified electrodes for boosting the sensitivity of electrochemical sensor devices

Silicon- or Carbon-Cored Multifunctional Carbazolyl Monomers for the Electrochemical Generation of Microporous Polymer Films

A series of four tetra- or octacarbazolyl-substituted, tetraphenylmethane/-silane monomers have been oxidatively coupled into microporous polymer networks (MPNs). Chemical polymerization with iron­(III) chloride gives bulk MPNs with BET surface areas (<i>S</i>_BET) of up to 1331 m² g^–1 (for the octacarbazolyl-substituted tetraphenyl­methane monomer). Slightly increased <i>S</i>_BET values result for the materials made from the octacarbazolyl monomers if compared to the tetracarbazolyl analogues, while the exchange of the central carbon by a silicon atom leads to decreased surface areas. The latter phenomenon might be related to electronic interactions of aromatic substituents through the silicon centers. This may cause a reduced reactivity of the carbazoles after the initial oxidative couplings and finally a reduced cross-linking density of the resulting MPNs. Moreover, electrochemical oxidative coupling enables the formation of thin polymer films on the working electrode. These films also show high <i>S</i>_BET values that are only slightly reduced if compared to the corresponding bulk MPNs. Electrochemical quartz microbalance measurements allow for an in-situ characterization of the electrochemical MPN generation. Finally, the electrochemical reduction of a series of nitroaromatic compounds (NACs) on MPN-modified glassy carbon electrodes is studied and applied for high sensitivity NACs detection up to the ppb range

Thiophene-Based Microporous Polymer Networks via Chemical or Electrochemical Oxidative Coupling

Four thiophene-based monomers have been synthesized by Stille- or Suzuki-type couplings followed by chemical or electrochemical polymerization into microporous polymer networks (MPNs) with high BET surface areas (<i>S</i>_BET). Similar <i>S</i>_BET values of up to 2020 and 2135 m² g^–1 have been determined for tetraphenyl­methane-cored bulk MPN powders and thin films, respectively. Electrochemical polymerization in boron trifluoride diethyl etherate (BFEE)/dichloromethane (DCM) mixtures allows for the generation of MPN films with optimized porosity. Moreover, an interesting effect of boron trifluoride on the connectivity of the monomeric units during electropolymerization is observed for 3-thienyl-based monomers. Finally, the electrochemical reduction of 1,3,5-trinitro­benzene at MPN-modified glassy carbon (GC) electrodes shows increased cathodic responses compared to nonmodified GC electrodes due to interaction between electron-deficient nitroaromatic analyte and electron-rich MPN film. The influence of the specific surface area of MPNs on the electrochemical response is also studied for this class of materials