Fluorinated donor-acceptor polymers blended with solid-state ionic liquids for highly sensitive and selective detection of volatile organic compounds.

Abstract

Solid-state ionic liquids (SILs), comprising cations with long-alkyl chains and anions containing fluorine atoms, have become essential for achieving electrochemical doping of π-conjugated polymers (π-CPs), as the formation of polarons is stabilized by the presence of fluorinated anions under applied bias. Nevertheless, phase separation on the scale of a few hundred nanometers between the polymers and SILs limits efficient doping and hinders intermolecular charge transport. In this study, we present a molecular design approach that incorporates electron-withdrawing fluorine atoms into the isoindigo unit of benzodithiophene-isoindigo (BI) copolymers. This targeted fluorination optimizes the surface energy of the polymer, facilitating the development of well-organized fibrillar nanostructures with improved order and connectivity when mixed with SILs. The optimized morphology enhances the migration of fluorinated anions from the SIL, which in turn promotes efficient electrochemical doping within the fluorinated BI matrix. Additionally, the electrochemical doping process is modulated by alcohol-based gases, yielding chemiresistors with outstanding gas selectivity. Of particular note, the fluorinated BI:SIL chemiresistor demonstrated an impressive response to 1-butanol, reaching a resistance change (ΔR/R₀) of 85.28% at 500 ppm and a limit of detection (LOD) of 513.6 ppb. These results underscore the potential of fluorinated π-CP/SIL blends to serve as adaptable platforms for scalable, selective, and environmentally sustainable organic sensing applications.