Fullerene-Doped Poly(ionic liquids) as Small Molecular Gas Sensors─Control of Intermolecular Interactions

Here, we investigate the interactions between five representative gaseous analytes and two poly(ionic liquids) (PILs) based on the sulfopropyl acrylate polyanion in combination with the alkylphosphonium cations, P_4,4,4,4 and P_4,4,4,8, and their nanocomposites with fullerenes (C₆₀, C₇₀) to reveal the potential of PILs as sensitive layers for gas sensors. The gaseous analytes were chosen based on their molecular size (all of them containing two carbon atoms) and variation of functional groups: alcohol (ethanol), nitrile (acetonitrile), aldehyde (acetaldehyde), halogenated alkane (bromoethane), and carboxylic acid (acetic acid). The six variations of PILs-P_4,4,4,4SPA (<b>1</b>), P_4,4,4,4SPA + C₆₀ (<b>1</b> + C₆₀), P_4,4,4,4SPA + C₇₀ (<b>1</b> + C₇₀), and P_4,4,4,8SPA (<b>2</b>), P_4,4,4,8SPA + C₆₀ (<b>2</b> + C₆₀), P_4,4,4,8SPA + C₇₀ (<b>2</b> + C₇₀)-were characterized by UV-vis and Raman spectroscopy, and their interactions with each gaseous analyte were studied using electrochemical impedance spectroscopy. Exposure of all PIL samples to acetaldehyde, bromoethane, and ethanol leads to a decrease in the diffusion coefficient, while exposure to acetic acid reveals an increase. Fullerene-doping significantly enhances the response to the analyte. Semiempirical quantum mechanical xTB-GFN2 calculations revealed that hydrogen bonding and proton transfer events play an important role during the detection process.