Design, Synthesis And Property Of Azo-Polymer With Photo-Responsive Function

In1937, S. Hartley first found that the collar of azobenzene could change fromorange red to yellow when azobenzen was irradiated by one special light. Since then,the different conformations of azobenzene, the cis-configuration and trans-configuration are gradually understood and cognized. The excellent isomerization ofthe two configuration of azobenzene is a subject of widespread concern. Till nowsome soft materials with photo-response moiety are chosen to construct artificialmuscles because they possess such necessary properties as good mechanicalflexibility, high corrosion resistance, and high molecular orders. Up to now, severaltypes of photo-response polymers have been developed as organic actuator materials,including polymer gel, movement of free-standing solid films, photo-inducedexpansion, shape memory polymers, and liquid-crystal polymer (LCPs). In the lastfive decades, regarded as well-known photo-response actuators, azobenzene and itsderivatives have been extensively investigated due to their photo-induced geometricisomerization. This kind of compounds possesses some special properties in theprocess of reversible photo-isomerization between cis-configuration and trans-configuration, reflected in their size, shape, polarity, refractive index, conductivity,solubility and so on. The isomerization of cis-trans configuration can induce masstransfer which can be roughly classified into three levels as illustrate. At themolecular level light generates trans-cis-trans isomerization which depletes thechromophore concentration in the direction of polarization, at the domain level thepolar chromophore movement reorients polar domains and at the mass level the light produces macroscopic movement of polymer the can be used to inscribe surface orbulk patterns. Based the mass transfer theory, photo-response molecules andpolymers with azobenzene moiety was first introduced to the field of micro-/nano-fabrication in1995by Rochon and Natansohn. Lots of literatures were reportedabout photo-induced surface patterning using azo-polymer.Although many related work in the preparation of photo-induced surfacepatterning using materials with azobenzene moiety were reported, some problemsstill exist as follows to be solved. The first problem is the issue of the formationmechanism of the photo-induced SRG. Generally, mass transfer theory is applicableto the azobenzene photoresponsive material, but the precise migration process andmigration patterns still don‘t have a certain answer to explain by now. It means thatthe exact mechanism of photo-induced SRG with azo-polymers is still notrecognized, which seriously hinders its deeper research and application in industry.The second problem is the issue of stability of photo-induced SRG. The thermalstability of the photo-induced surface patterning using azo-polymer is totallydepended by the glass transition temperature (Tg) of the material itself. And at thesame time, the Tg of most of azo-polymer are widely concerned not high enough, sothe stability of the photo-induced patterning is not good enough. Besides the thermalstability, general acid, alkali, and organic solvent can also destroy pattern indeed,which seriously affects the application foreground of photoresponsive materials withazobenzene moiety.Based on the current problems about photoresponsive materials with azobenzenemoiety, herein, our thesis research is focus on the following three aspects:1. Develop a kind of novel azobenzene materials used in photo-induced pattern andexplore its mechanism. We design and synthesize a conjugated polymer withazobenzene moiety in the main chain, named PFAzo. Then, the SRG pattern isformed on the surface of the PFAzo film by interfering laser beam irradiated.From the knowledge obtained, the mechanism of the photo-induced patternformation in the present system is first assumed by us as follows. After beingirradiated by interfering laser beam, the CP chains transform from a rigid-rodstructure of trans-configuration to a random coil of cis-configuration. This conformational change induces a large local stress which drives the polymerchain to transfer from light irradiation part to dark part. Based on this process,thus the highly contrast surface pattern is formed.2. Explore a novel method to obtain stable photo-induced pattern by azobenzenematerial. We design and synthesize an electrochemical deposition (ED) precursornamed as DFCzAzo, which contains both electroactive carbazole groups andphoto-controlled azobenzene moiety. The polymerization reaction occurs amongthe radical cations with deposition of the cross-linked polymer film onto theelectrode. The highly cross-linked network results to the excellent stability of thephoto-induced nano-structures. We believe that the present photo-controlledsystem will provide a novel concept for creation of steadily cross-linked ED filmand will play an important role in many potential applications, such as the designof novel optical devices, and micro-/nano-scale sculpture.3. Investigate the feasibility of conjugated microporous polymers (CMPs)containing azobenzene moiety in terms of molecule capture. We design andsynthesize a novel ED precursor named as DTCzAzo, which contains both eightfunctionality electroactive carbazole groups and photo-responsive azobenzenemoiety. A highly cross-linked three-dimensional pore structure of the polymericfilm is produced by the electrochemical deposition method. And the film still hasa rigid isomerization property just as the polymer spinning coated film. Thediameter of pore structure changes in the process of the trans-to-cisisomerization, to capture organic molecules with the suitable molecules size.Then we achieve the target of fabricating a molecular cage.