Reversible photoswitching of proton conduction in hetero‐smectic lamellar structures formed by side‐chain liquid crystalline copolymer thin films

Abstract Spatiotemporal control of ion conductivity is a key issue for creating emerging fields of functional ion‐conducting nanomaterials. In the present paper, we demonstrate the formation of hetero‐smectic lamellar structures, which are formed by nanosegregation of hydrophobic liquid crystalline (LC) azobenzene side chains and hydrophilic acrylic acid side chains via polymer main chains in side‐chain LC (SCLC) copolymers, and the reversible photoswitching of the proton conductivity. Proton‐conducting SCLC copolymers with different acrylic acid contents are synthesized by free‐radical copolymerization. The LC nature of the synthesized polymers is investigated by polarized optical microscope observation, differential scanning calorimetry and X‐ray scattering measurements. Ultraviolet (UV)–visible absorption spectroscopy and grazing incidence X‐ray scattering measurements reveal the hetero‐smectic lamellar formation of SCLC copolymer thin films. Proton conductivity of the polymer thin films is evaluated by impedance spectroscopy measurements under different temperatures and relative humidity conditions with sequential UV light irradiation. These results indicate that stable and reversible photoswitching of the proton conductivity around one order of magnitude is attributed to the trans – cis photoisomerization of azobenzene side chains by UV light irradiation. These results offer the opportunity for applications of photo‐functional nanomaterials including emerging biomimetic ionic signal transduction devices and neuromorphic devices. © 2024 Society of Chemical Industry.