Guard Cell‐Inspired Ion Channels: Harnessing the Photomechanical Effect via Supramolecular Assembly of Cross‐Linked Azobenzene/Polymers

Abstract

Stimuli‐responsive ion nanochannels have attracted considerable attention in various fields because of their remote controllability of ionic transportation. For photoresponsive ion nanochannels, however, achieving precise regulation of ion conductivity is still challenging, primarily due to the difficulty of programmable structural changes in confined environments. Moreover, the relationship between noncontact photo‐stimulation in nanoscale and light‐induced ion conductivity has not been well understood. In this work, a versatile design for fabricating guard cell‐inspired photoswitchable ion channels is presented by infiltrating azobenzene‐cross‐linked polymer (AAZO‐PDAC) into nanoporous anodic aluminum oxide (AAO) membranes. The azobenzene‐cross‐linked polymer is formed by azobenzene chromophore (AAZO)‐cross‐linked poly(diallyldimethylammonium chloride) (PDAC) with electrostatic interactions. Under UV irradiation, the trans‐AAZO isomerizes to the cis‐AAZO, causing the volume compression of the polymer network, whereas, in darkness, the cis‐AAZO reverts to the trans‐AAZO, leading to the recovery of the structure. Consequently, the resultant nanopore sizes can be manipulated by the photomechanical effect of the AAZO‐PDAC polymers. By adding ionic liquids, the ion conductivity of the light‐driven ion nanochannels can be controlled with good repeatability and fast responses (within seconds) in multiple cycles. The ion channels have promising potential in the applications of biomimetic materials, sensors, and biomedical sciences.

Recent Development of Photochromic Polymer Systems: Mechanism, Materials, and Applications

“…2 A-iv). The azobenzene cross-linked polymer (AAZO-PDAC) was used to create photoswitchable ion channel designs inspired by guard cells [ 41 ]. Under UV irradiation, trans azobenzene was converted to cis , compressing the volume of the polymer network; conversely, the structure was restored in the dark.…”

“…(B) Graphical illustrations of the photoswitchable polymer system, in which the photomechanical properties and on-demand ionic conductivity can be achieved via light irradiations. Reproduced with permission from [ 41 ]. Copyright 2023, John Wiley & Sons Inc. (C-i) Schematic diagram of synthesis of photochromic dendrimers.…”

Halogen effect in photomechanical molecular crystals

“…Furthermore, photomechanical materials can be used in drug delivery systems, biomedical imaging, implantable devices, sensing, and monitoring. 162 The release of the drugs loaded on the photomechanical crystals can be controlled by light with a specific light wavelength, which enables the precise and localized treatment of diseases. The photo-induced mechanical and luminescent responses can act as contrast agents to enhance existing imaging modalities such as ultrasound or magnetic resonance imaging.…”

Photo-Healable Fabrics: Achieving Structural Control via Photochemical Solid–Liquid Transitions of Polystyrene/Azobenzene-Containing Polymer Blends

“…Azobenzene, a well-known photoswitchable molecule, can undergo trans - cis photoisomerization upon UV irradiation . Applying azobenzene to polymer chains, versatile phenomena manipulated via light have been investigated, especially tuning their physicochemical properties. − For instance, de Luna et al have reported a supramolecular hydrogel based on azobenzene anions and cations with long alkyl chains, showing the healability after mechanical vibration . Meanwhile, Zhou et al have presented a novel light-switchable adhesive with a tunable T g of azobenzene-containing polymer upon UV irradiation …”