Photomodulated Morphologies in Halogen Bond–Driven Assembly during Gel–Sol Transition

Abstract

Photoresponsive supramolecular gels with various applications are being constantly pursued; however, achieving well‐defined morphology changes of gels via light irradiation remains a formidable challenge. In this study, a gel is prepared through halogen bond between azopyridine‐containing Azopy‐C10 and 1,4‐tetrafluorodiiodobenzene. The gel exhibits gel–sol transition due to trans–cis isomerization of the azopyridine moiety upon UV irradiation. During this transition, the morphologies vary from flake to fluffy bobble‐like and finally to peony‐like with increasing exposure time, which is difficult to achieve in traditional assembly systems. The microstructure change is attributed to the variations of cis‐isomer content and halogen‐bonding strength. The supramolecular gel provides a novel method to achieve photomodulated morphologies and broadens the applications of such kind of materials, ranging from information storage to high‐tech anticounterfeit.

Reversible photo-responsive gel–sol transitions of robust organogels based on an azobenzene-containing main-chain liquid crystalline polymer

“…9 In fact, the obtained K tc linearly depends on the light intensity at a specic irradiation wavelength. 24 When the intensity of UV light irradiation was only about one-tenth of the most intensities listed in Table S2 (ESI †), Azo-mLCP could reach a photo-stationary state with a smaller t N. 9,[26][27][28][29][30][31][32] Compared with most azobenzene-containing polymers and small molecules, our Azo-mLCP displayed a larger constant of photoisomerization under a lower UV light intensity. This was mainly attributed to the coupling effect between the photoisomerization reaction and the conformation of the liquid crystal polymer chain being stronger when the photoresponsive group is located on the main chain.…”

One-Pot Route to X-perfluoroarenes (X = Br, I) Based on FeIII-Assisted C–F Functionalization and Utilization of These Arenes as Building Blocks for Crystal Engineering Involving Halogen Bonding

“…Until now, the most common synthons for these purposes were based on linear XB/XB-bifunctional species (X = Br, I) such as two-center dihalides X 2 , − di-X-perfluoroarenes, ,− XCCX, − or bent XB/XB synthons such as haloalkanes. − Cocrystallization of all these XB/XB-donating building blocks with appropriate bifunctional XB/XB acceptors in many reported instances leads to well-organized supramolecular networks. Apart from their application in crystal engineering, mono- and di-X-perfluoroarenes (X = Br, I) have been used in the modulation of photophysical − properties, stabilization of explosives, gels, micelles, nanowire preparation, and so on.…”

Recent Progress in Azopyridine-Containing Supramolecular Assembly: From Photoresponsive Liquid Crystals to Light-Driven Devices

“…This method provides a useful strategy for the preparation of a visible-light-triggered phase transition of supramolecular materials, in particular application scenarios, from energy conversion to information storage. Hu and co-workers recently reported an AzPy-containing liquid-crystalline gel through X-bonding between an AzPy-C10 and 1,4-tetrafluorodiiodobenzene (TFDIB), as shown in Figure 17a [93]. Upon irradiation with UV light, the gel shows a gel-sol transition as well as a morphology change from flake to peony-like due to the light-induced transcis isomerization of the AzPy moiety.…”

“…As suggested, it is better to use donors and acceptors with long-lived metastable states and liquid-crystal phases that occur close to room temperature with low clearing points for stabilizing the photoinduced isotropic state of X-bond complexes. Hu and co-workers recently reported an AzPy-containing liquid-crystalline gel through X-bonding between an AzPy-C10 and 1,4-tetrafluorodiiodobenzene (TFDIB), as shown in Figure 17a [93]. Upon irradiation with UV light, the gel shows a gel-sol transition as well as a morphology change from flake to peony-like due to the light-induced trans-cis isomerization of the AzPy moiety.…”