Synthesis And Gelation Properties Of The Gelators Based On Azobenzene

As a kind of self-assembly materials,supramolecular gels could form ordered 3D network microstructure by noncovalent interactions such as hydrogen bonding,?-? stacking,electrostatic interactions and so on,comprising a fibrous solid-like phase immobilising a much larger liquid volume.In the case of a hydrogel the liquid component is water,while for an organogel it is an organic solvent.Gelators have many unique features,such as the design of molecular structure and the flexibility to respond to external stimuli.Recently,attention has been shifted to how to functionalize the gelators through adding functional groups or reaction groups.Photoresponsive azobenzene moieties have been used in gelators.There are some fundamental issues relate to the gelation process in supramolecular gels,such as the solvents,the structure of gelators and the synergism between them and so on.In this paper,seven gelators based on azobenzene were designed and synthesized.The gelation properties and photoresponsive behavior were investigated.The details are summarised as follows:1.Seven gelators were synthesized through using 4,4'-dihydroxyazobenzene,4,4'-azodibenzoic acid,3,3'-dimethylbenzidine,4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenylmethane as raw materials.Molecular structures have been confirmed.2.The optical properties of gelators and the photo-response of gels were studied by spectroscopy methods.The photo-induced isomerization of azobenzene unit can be confirmed by monitoring the UV-visible spectroscopy evolution of gelator dilute solution and gel phase.Due to the difference of molecular structures,azobenzene units of gelators require different energy to transition.Their photoresponsive time is different.The photoinduced trans-to-cis isomerization takes place and eventually brings about the gel-sol transition with the change of colors in gels of Azo-1,Azo-6 and Azo-7.Compared with the dilute solution,the UV-visible spectroscopy of gels showed a certain degree of blue shift.It indicated that gelators formed H-aggregates in solvents.3.The morphology of xerogels and sols in a variety of solvents were observed by using the SEM.The micro-structure of xerogels strongly depends on the polarity of gelling solvents.Compared with the xerogels,the micro-morphologys of sols have obvious change.To sum up,the structure of the gelators plays a key role in the system for the gel performance and optical properties.The solvent type has a key influence on microstructure and light response performance of the gel system.By summarizing the characteristics of molecular structure,it provides valuable reference for preparing more controllable light-response gel.