Reversible Ion‐Conducting Switch in a Novel Single‐Ion Supramolecular Hydrogel Enabled by Photoresponsive Host–Guest Molecular Recognition

Abstract

because it can afford remote and precise control over the properties of hydrogels. [5] In recent years, a series of photo responsive hydrogel-based functional materials have been developed that show a number of emerging features, such as fluorescent, mechanical, and adhesive properties. [6][7][8][9][10] However, changing the conductivity of hydrogels by illuminationmediated ionic migration represents a promising yet challenging photoconductive property [11][12][13][14][15][16] that could be applied in many fields, including photo detectors, [17] the simulation of biophotoelectric signals, [18] and light control circuits. [19] Because of the difficulty of modulating the free movement of ions, it seems impossible to achieve photo controlled ionic conductivity in hydrogels by using a chemical strategy. In a few research studies, [20][21][22][23] the photo conductivity of hydrogels was realized through the introduction of traditional photo conductive electronic materials into the systems via a physical approach. For example, Zhu and co-workers successfully fabricated a 3D hydrogel network of titanium dioxide (TiO 2 )-graphene using a simple one-pot method; this network exhibited enriched adsorption-photoelectro catalytic degradation of low-concentration bisphenol A. [21] Ray and co-workers A novel ion-conducting supramolecular hydrogel with reversible photoconductive properties in which the azobenzene motif, α-cyclodextrin (α-CD), and ionic liquid are grafted onto the gel matrix is reported. Hostguest interactions with different association constants between α-CD and azobenzene or the anionic part of the ionic liquid can be readily tuned by photoinduced trans-cis isomerization of the azobenzene unit. When irradiated by 365 nm light, α-CD prefers to form a complex with the anionic part of the ionic liquid, resulting in decreased ionic mobility and thus high resistance of the hydrogel. However, under 420 nm light irradiation, a more stable complex is again formed between α-CD and trans-azobenzene, thereby releasing the bound anions to regenerate the low-resistive hydrogel. As such, remote control of the ionic conductivity of the hydrogel is realized by simple host-guest chemistry. With the incorporation of a logic gate, this hydrogel is able to reversibly switch an electric circuit on and off by light irradiation with certain wavelengths. The concept of photoswitchable ionic conductivity of a hydrogel mediated by competitive molecular recognition is potentially promising toward the fabrication of optoelectronic devices and applications in bioelectronic technology. HydrogelsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.Photoresponsive hydrogels have attracted broad interest as functional materials to enable drug delivery systems, [1] cell culture substrates, [2] permeable membranes, [3] and microactuators. [4] Compared with other stimuli-responsive mechanisms, light irradiation has particular advantages and promising applications

Cucurbiturils brighten Au nanoclusters in water

“…Host-guest self-assembly, typically the encapsulation behavior between small motifs and macrocycle molecules bearing cavities with a certain size, has received extensive attention in molecular recognition and stimuli-responsive systems. [1][2][3][4][5][6][7][8] Remarkably, driven by multiple non-covalent interactions such as ion-dipole, hydrophobic and H-bonding effects, macrocyclic cucurbit[n]urils (CB[n], n ¼ 5-8, typically) exhibit a robust binding strength with elaborately tailored guests to form stable binary and ternary host-guest complexes in aqueous solutions. 9,10 In the past two decades, the advancements in CB[n]based host-guest self-assembly have greatly facilitated the design of functional materials ranging from single molecules to various nanostructures.…”

Design Principles for Aqueous Interactive Materials: Lessons from Small Molecules and Stimuli‐Responsive Systems

“…Huang et al reported an ion‐conducting supramolecular hydrogel based on alpha‐cyclodextrin (α‐CD), an azobenzene unit and ionic liquid which were grafted onto a gel matrix 40. The resulting gel was photoresponsive on account of the different association constants between cis ‐ and trans ‐azobenzene derivatives toward α‐CD.…”

Driving Smart Molecular Systems by Artificial Molecular Machines

“…Polymers, representing an important platform for the combination of nanoscale chemistry and macroscopic objects, have been widely researched for potential applications in material science . The introduction of stimuli‐responsive molecular machine units into polymer systems to fabricate novel materials with advantageous properties such as self‐healability, high stretchability, and recyclability has drawn increased attention, while the introduction of responsive units may also endow these systems with controllable regulation …”