Study On Morphology Of Seesaw-shaped Amphiphilic Assembly

Supramolecular chemistry research area is involving many fields such as physics,chemistry,and biology.In aggregated structures,molecules are held together using a variety of weak non-covalent interactions.In the past few decades,scientists have used a variety of methods to build series of supramolecular nanostructures with various specific functions from zero to three dimensions.Among many nanomaterials,organic nanotubes have the characteristics of relatively long diameters,easy chemical modification on the inner and outer surfaces,and hollow interior space,so they have become hot spots in the research of nanomaterials.Molecular self-assembly is an important method for preparing organic nanotubes.Prior to this,researchers have fully studied nanotubes,which are based on continuous homogeneous tube wall structures.Here,we report unique supramolecular tubular bamboo-culm structures by self-assembly seesaw-shaped aromatic amphiphile,in which the hollow tubular interior was separated periodically by nodes per 1.3 nm.Addition of trans-azobenzene as a guest made the tubules to be interconnected to hierarchical sheet.When UV was irradiated to induce an isomerization from trans-azobenzene and its cis-isomer,the hierarchical sheet structures were disassembled into their constituent tubules because of weaken lateral association by cis-azobenzene.The transformation from cis-isomer to trans-azobenzene in dark environment induce the hierarchical sheet assembly again,indicative of reversible switching behavior between tubules and sheets.This paper will elaborate on this issue:In the first part,we introduced that the seesaw-like amphiphilic molecules form nanotubes with uniform pores in the tube wall in a mixed solution of methanol and water.We focused on the special configuration of seesaw molecules and the arrangement of bamboo flute-shaped nanotubes in polar solutions.We first designed and synthesized amphiphilic aromatic molecules.This amphiphilic molecule has a unique space-like configuration similar to a warped plate,and can self-assemble into nanotubes in a mixed solution of 40% methanol and 60% water.This is a new type of nano-tube structure.We used dry transmission electron microscopy and atomic force microscopy to characterize its morphology,to prove that the hollow bamboo flute-like shape with holes every 1.3 nanometers is evenly distributed on the wall of a tube ofaround 7 nanometers in diameter.Combining with the molecular size,we can determine that the bamboo-flute-like assembly is a soluble monolayer supramolecular aggregate formed by four seesaw-like molecules stacked by π–π to form a nano-cyclic structure along the axial direction through lateral interaction.Compared with classic organic nanotubes,bamboo-flute-shaped nanotubes have a larger specific surface area and more modification sites.This provides new ideas for the design of new nanotubes.Part 2: We add azobenzene as guest molecule to the bamboo-flute-like nanotube system.Due to the hydrophobic interaction,trans-azobenzene can enter the voids of bamboo-flute-shaped nanostructures and co-assemble with them to form a two-dimensional sheet structure.We used dry-state transmission electron microscopy and atomic force microscopy to characterize its morphology,and proved that the thickness was 7.2 nm.Combining the dimensions of bamboo flute-shaped nanotubes assembled with pure molecules under the same solvent conditions,we can know that the sheet structure is formed by multiple nanotubes arranged horizontally and connected by guest molecules.We use the photoisomerization properties of azobenzene to irradiate the co-assembly with ultraviolet light.Due to the different sizes of azobenzene cis-trans isomers,the two-dimensional sheet structure was destroyed and the tubular aggregates reappeared.Based on the light regulation achieved by covalently linking to azobenzene function group,we use non-covalent forces to control the morphology by light-regulated supramolecular co-assemblies.Part 3 Based on seesaw molecules assembled behaviors,we tried to control morphology by adding functional group.We choose methoxy group to link to seesaw molecules.This molecule can be assembled to vesica.For next stage,we tried to use this material to capture,transfer and release guest molecule.