Yaning He

Epoxy-based azo polymers: synthesis, characterization and photoinduced surface-relief-gratings

Abstract Epoxy-based azo polymers with three kinds of backbones, different types of azo chromophores, and selected degrees of functionalization (DFs), were synthesized through a post-polymerization azo-coupling scheme. The T g s of the azo polymers were found to be considerably influenced by the substituents on the 4-positions of the azobenzene units and increased with the increase of the DFs of the polymers. Surface-relief-gratings (SRGs) were induced on the polymer films by interferenced Ar + laser beams. With the same irradiating light intensity and approximately equal film thickness, the rates of SRG formation were found to be significantly dependent on the electron-withdrawing groups on the 4-positions of the azobenzene units. For the polymers with the same type of azo chromophores and backbone structure, the inscription rates increased with the increase of the DFs. Meanwhile, the backbone structure also exhibited some effect on the inscription rates through the ways such as changing chromophore loading density or main-chain rigidity.

Photo-switched wettability on an electrostatic self-assembly azobenzene monolayer

A simple electrostatic self-assembly technique was used to fabricate a photo-switched azobenzene monolayer, on which superhydrophobicity and a large reversible CA change could be realized.

Hexabenzocoronene graphitic nanotube appended with dithienylethene pendants: photochromism for the modulation of photoconductivity.

[*] Dr. Y. Yamamoto, Dr. W. Jin ERATO-SORST Nanospace Project Japan Science and Technology Agency (JST) 2-41 Aomi, Koto-ku, Tokyo 135-0064 (Japan) E-mail: yamamoto@nanospace.miraikan.jst.go.jp jin@nanospace.miraikan.jst.go.jp Prof. T. Aida, Dr. Y. He Department of Chemistry and Biotechnology School of Engineering, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) E-mail: aida@macro.t.u-tokyo.ac.jp Dr. T. Fukushima Advanced Research Institute, RIKEN 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)

Fast Photoinduced Large Deformation of Colloidal Spheres from a Novel 4-arm Azobenzene Compound

A novel 4-arm shaped amphiphilic azobenzene compound was synthesized. The tetraphenylethylene (TPE) core precursor was prepared and further modified by azo coupling reaction at the four peripheral groups. Colloidal spheres could be directly prepared by self-assembly of the prepared amphiphilic azobenzene compound in selective solvents (THF/H2O), which were characterized by using transmission electron microscopy. The colloid diameters could be controlled by adjusting the initial compound concentration and water-adding rate in the preparation processes. By irradiation with visible linearly polarized LED light (450 nm), fast photoinduced deformation of the colloidal spheres along the polarization direction was observed. A very large deformation degree (l/d > 4) could be easily obtained.

Hollow microspheres of amphiphilic azo homopolymers: self-assembly and photoinduced deformation behavior

A unique way to fabricate hollow microspheres by using an amphiphilic azo homopolymer (BP-AZ-CA) and photoinduced deformation behavior of the hollow structures in the solid state are reported.

Azo Polymer Colloidal Spheres Containing Different Amounts of Functional Groups and Their Photoinduced Deformation Behavior

In this work, colloidal spheres composed of azo polymers with different chromophore loading densities were prepared, and their photoinduced deformation behavior was studied. The colloids were constructed by using a series of amphiphilic epoxy-based random copolymers containing 4-carboxylazobenzene functional groups with different degrees of functionalization (DFs). The colloidal spheres were fabricated through gradual hydrophobic aggregation of the polymeric chains in tetrahydrofuran-H2O dispersion media, which was induced by gradually adding water into the systems. The colloidal spheres were characterized by using transmission electron microscopy and dynamic light scattering. The photoinduced deformation behavior was studied by irradiating the colloidal spheres with a linearly polarized Ar+ laser beam. Results showed that the critical water content (CWC) for the colloid formation is related to the DF of the polymers, and CWC increases with the increase of DF. The hydrodynamic diameter of the colloidal spheres is also related to the DF of the polymers. When the DF of the polymers increases, the average size of the colloids gradually decreases. The hydrodynamic diameter of the colloidal spheres increases as the water dropping rate decreases. When the dropping rate is below 20 microL/s, the size of the colloidal spheres increases abruptly as the dropping rate further decreases. Upon the linearly polarized Ar+ laser beam irradiation, the colloids composed of polymers with different DFs can all be elongated along the polarization direction of the laser beam. As DF increases, the deformation degree characterized by the axial ratio (l/d) almost linearly increases. These observations can give some insight into the photoinduced deformation mechanism and can be used to construct colloids with different sizes and photoresponsive ability.

Amphiphilic diblock copolymer with dithienylethene pendants: synthesis and photo-modulated self-assembly.

In this work, an amphiphilic diblock copolymer (PEG(43)-b-PSDTE(29)) bearing photochromic dithienylethene (DTE) pendants is synthesized by reversible addition fragmentation chain transfer radical polymerization. The diblock copolymer was characterized by spectroscopic methods and gel permeation chromatography. The analyses proved the well-defined structure and narrow molecular weight distribution of the diblock copolymer. The DTE pendants could undergo reversible photoisomerization between their open and closed forms in solution when irradiated with UV and visible light as indicated by (1)H NMR and UV-vis spectroscopy. Hollow vesicle-like structures were formed by gradually adding deionized water to the colorless PEG(43)-b-PSDTE(29open) (DTE in open form) tetrahydrofuran solution. Under the same conditions, the aggregates formed in the blue PEG(43)-b-PSDTE(29close) (DTE in closed form) solution were colloidal spheres with solid interiors. The isomerization of DTE pendants could cause the deformation of the vesicle-like structures. The above results demonstrate a kind of novel photo-modulated self-assembly behavior of the amphiphilic diblock copolymer, which could be used for drug-delivery and other applications.

Synthesis of Y-shaped amphiphilic copolymers by macromolecular azo coupling reaction

The synthesis of AB2 Y-shaped amphiphilic block copolymers by macromolecular azo coupling reaction is reported. The hydrophobic block with the functional group at the end of the polymeric chain was prepared by controlled radical polymerization methods such as RAFT and ATRP. The hydrophilic block with diazonium salt group was obtained by the diazotization of V-shaped aniline-functionalized PEG. Then Y-shaped block copolymers were easily prepared through macromolecular azo coupling reactions between the abovementioned two polymeric blocks. The results of experiments showed that the position of the functional group suitable for azo coupling reaction in the polymeric chain has considerable effect on the efficiency of macromolecular azo coupling reaction. It was easier for the macromolecular diazonium salts to attack the functional groups when they were at the end of the macromolecular chains instead of in the middle. The self-assembly properties of the obtained Y-shaped amphiphilic block copolymers were also studied. Colloidal spheres were prepared by gradual hydrophobic aggregation of the polymeric chains in a THF–H2O dispersion medium.

Photoluminescent nematic liquid crystalline elastomer with a thermomechanical emission variation function.

Nematic liquid crystalline elastomer (LCE) microactuators are developed, showing simultaneous thermomechanical deformation and photoluminescence (PL) emission variation functions. The microactuators are prepared by a method combining soft-lithography and photo-polymerization/crosslinking. 1,4-Bis(α-cyano-4-methoxystyryl)benzene as the PL dye is synthesized, characterized, and introduced into LCEs as a dopant in the preparation process. During the heating process, PL emission of the LCE micropillars under blue light excitation becomes significantly weak when the micropillars contract. When cooling down, the emission completely recovers as the micropillars stretches back to their original shape. The PL intensity variation at the transition is proved to be related to the thermomechanical deformation.

Photoinduced orientation and cooperative motion of three epoxy-based azo polymers

In this work, photoinduced orientation of three epoxy-based polymers bearing different type azo chromophores was studied. The epoxy-based azo polymers were synthesized through post-polymerization azo-coupling reactions based on an epoxy-based precursor polymer (BP-AN), which was synthesized by the step polymerization between bisphenol-A diglycidyl ether and aniline. The chromophore orientation and cooperative motion of the main-chain groups were studied by birefringence characterization, polarized infrared spectroscopy, and two-dimensional (2D)-IR correlation spectroscopy (COS). The results show that the orientation behavior of the epoxy-based azo polymers is closely related with the electron-withdrawing groups on the azo chromophores. The azo polymer BP-AZ-CN, which contains azo chromophores with cyano as the electron-withdrawing group, shows the fastest birefringence growth rate. The azo polymer BP-AZ-CA, containing carboxyl as the electron-withdrawing group, possesses high birefringence residual value and the highest saturated orientation degree in the series. Cooperative motion between azobenzene moieties and non-photochromic polymer backbone was revealed by polarized FTIR and 2D-IR COS. The photoinduced anisotropy is a result of the orientation of both azo chromophore and polymer main-chain. The understanding of the structure–property relationships can be used to develop materials with better performance for data storage and other applications.