Supramolecular Functional Materials Based On The Azopyridine Derivatives

The self-assembling of functional molecules into supramolecular structures is a powerful approach toward the development of new materials and nanoscale devices. Azopyridine (AzPy) derivatives have aroused much interest because of their great advantages of possessing both the light-activity related to azobenzene showing the reversible trans/cis isomerization upon photoirradiation and the capability of self-assembly through pyridyl groups. Meanwhile, Azpy derivatives exhibit photothermal effect upon UV irradiation with a high intensity.Although AzPy derivatives have distinguished features, the research on the AzPy derivatives limits in low-molecular-weight self-organization fibers and the photoresponsive liquid crystals. In this paper, combining the photoresponsive properties and the self-organization feature of AzPy, the functions and applications have been explored and developed, the results of which are listed following:(1) Photothermal effect of AzPy compounds and their analogue azobenzene compounds were studied systematically. Under the same conditions, the azopyridine compounds showed higher photothermal conversion efficiency than the analogue azobenzene compounds. Two possible applications were proposed for the photothermal effect of AzPy compounds. One was intelligent stickup technology, and the tensile strength between two glass sides was photocontrolled to be as high as0.661MPa. The other was photo-driven movement with bilayer films composed of one A12AzPy/PVA composite film, and photoinduced bending was successfully obtained due to volume change caused by the photothermal effect.(2) A series of photoresponsive halogen-bonded liquid crystals (LCs) were first constructed using molecular iodine or bromine and AzPy compounds, which showed interesting properties of photoinduced phase transition upon UV irradiation. In addition, bromine-bonded LCs were first obtained with high mesophase stability. Meanwhile, the effect of terminal alkyl chain of the azopyridine compounds on the liquid crystal behaviors was also been studied.(3) Supramolecular self-organization behaviours of one AzPy compound were systematically studied in a series of inorganic acids and various organic solvents. Different morphologies were observed in diverse environment. The acid dissociation constant has a critical affect on the self-assembly process. Besides, the organic solvent also influenced the process of fiber formation. For instance, self-organized gelation is easier to form in acetone. Meanwhile, the effect of terminal alkyl chain of the azopyridine compounds on the gelation ability has also been studied. When the concentration of the azopyridine compounds increase to60mg/mL, the azopyridine compounds which the terminal alkyl chain greater than or equal to12could make acetone gelation and with increase of the terminal alkyl chain of the azopyridine compounds as gelator, the gelation ability became more and more stronger. Then, possible schematic illustration for fabrication of the supramolecularly self-assembled fibers was proposed based on TEM and XRD measurements. That is, visible micron-fibers were made up of nanofibers through stacking interaction forces of azopyridine chromophores.