Azobenzene Molecular Machine: Light-Induced Wringing Gel Fabricated from Asymmetric Macrogelator

Abstract

To develop light-triggered wringing gels, an asymmetric macrogelator (1AZ3BP) was newly synthesized by the chemically bridging a photoisomerizable azobenzene (1AZ) molecular machine and a biphenyl-based (3BP) dendron with a 1,4-phenylenediformamide connector. 1AZ3BP was self-assembled into a layered superstructure in the bulk state, but 1AZ3BP formed a three-dimensional (3D) network organogel in solution. Upon irradiating UV light onto the 3D network organogel, the solvent of the organogel was squeezed and the 3D network was converted to the layered morphology. It was realized that the metastable 3D network organogels were fabricated mainly due to the nanophase separation in solution. UV isomerization of 1AZ3BP provided sufficient molecular mobility to form strong hydrogen bonds for the construction of the stable layered superstructure. The light-triggered wringing gels can be smartly applied in remote-controlled generators, liquid storages, and sensors.

Azobenzene-Equipped Covalent Organic Framework: Light-Operated Reservoir

“…In particular, the merits of photoresponsive materials capable of capturing and releasing guest molecules in response to light irradiation have garnered considerable regard. ,,− Azobenzene is one of the most common light-responsive molecular switches that can be reversibly switched between its trans and cis isomers by applying light of a particular wavelength. Azobenzene-based compounds form the cis isomer upon exposure to UV light, , while the reverse trans -isomerization reaction can be achieved upon visible-light irradiation. − This photoisomerization process induces a large geometrical change, with the nonplanar cis conformer having a shorter distance between the aryl termini ( d 4–4′ ≈ 6 Å) compared to the planar trans conformer ( d 4–4′ ≈ 9 Å). , On account of these significant structural and geometrical changes, photoactive azobenzene molecules were widely incorporated into a variety of supramolecular polymeric materials, − gels, metal organic frameworks, ,,,− and other nanostructures. , …”

“…22−24 This photoisomerization process induces a large geometrical change, with the nonplanar cis conformer having a shorter distance between the aryl termini (d4−4′ ≈ 6 Å) compared to the planar trans conformer (d4−4′ ≈ 9 Å). 24,25 On account of these significant structural and geometrical changes, photoactive azobenzene molecules were widely incorporated into a variety of supramolecular polymeric materials, 26−32 gels, 33 metal organic frameworks, 20,23,24,34−36 and other nanostructures. 37,38 Covalent organic frameworks (COFs) 39−42 are a class of robust two-and three-dimensional extended network materials that are known for their artistic structures and potential for a wide range of applications, 43 such as gas storage, 44 separation, 45 chemical sensing, 46−50 and catalysis.…”

Fluorescent Azobenzene-Containing Compounds: From Structure to Mechanism

“…The reversible cis-trans transformation of azobenzenes is a remarkable photochemical phenomenon, which has been utilized for making smart switches [8,[14][15][16][17][18][25][26][27][28], selfassembly materials [29][30][31][32][33], light-responsive liquid crystals [3,8,[33][34][35], gels [4,[36][37][38][39] etc. Upon exposure to UV light, trans-azobenzene transforms into its cis-isomer.…”

Controlling Supramolecular Structures of Drugs by Light

“…In fact, as the water was macroscopically separated throughout the structure (visible observation), we expect nanosegregation of aliphatics and the respective ion pairs dominating self-assembly in bulk after irradiation. Back-conversion of the cis -azobenzene in the trans -isomer over time reverted the process; i.e., water was again integrated into the gel structure (observed visually), and the thermodynamically stable structure was attained again as seen before by others. , However, the limited data set (SAXS and nonoriented multidomain samples) allows for qualitative interpretation but not for deriving a precise structure model of the supramolecular assembly. Figuratively, the gel layer formed photoswitchable molecular sponges experiencing a structural transition in response to light, accompanied by corresponding color changes from yellow ( trans ) to dark red ( cis ).…”