• Bulletin of the Korean Chemical Society
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• v.23 no.7
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• pp.957-963
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• 2002

We successfully synthesized the addition-type polynorbonenes (PNB) exhibiting photochromic properties and excellent thermal stability. Three norbornene-based monomers with different azobenzene moiety (R=NO2, H,OCH3) were synthesized by transesterification method. The corresponding PNB copolymers were synthesized by transition metal-catalyzed addition polymerization method, and characterized by GPC, UV-Vis spectroscopy, NMR, and thermal analysis. For comparison of the photochromic properties depending on the rigidity of polymer backbone, we prepared the polymethylmethacrylate (PMMA) copolymer with the corresponding azobenzene moiety. We investigated the photoisomerization behavior by means of optical muitichannel analyzer with Xe lamp as well as real-time UV-Vis spectroscopy with high-pressure mercury lamp. Among three PNB copolymers, a polymer with azobenzene (R=H) was the most adaptable for observation of photoisomerization behavior. It was found that the rate of photoisomerization and relaxation depended on the structure of azobenzene chromophore, rather than that of polymer backbone.

• Bulletin of the Korean Chemical Society
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• v.20 no.10
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• pp.1186-1194
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• 1999

Photoresponsive side chain polymers containing aminonitro azobenzene were synthesized for studying optically induced birefringence. Four different copolymers were prepared using methacrylate, a-methylstyrene, and itaconate monomer. Two copolymers are totally amorphous and the other two are liquid crystalline in nature. Trans-to-cis photoisomerization was observed under the exposure of UV light with UV-VIS absorption spectroscopy. Reorientation of polar azobenzene molecules induced optical anisotropy under a linearly polarized light at 532 nm. The dynamic parameters of optically induced birefringence let us compare the effect of polymeric structure on the rate of growth and decay of the birefringence. Besides the effect of glass transition temperature on the dynamics of photoinduced birefringence, we focused our interests on the geometrical hindrance of polar azobenzene molecules and cooperative motion of environmental mesogenic molecules in the vicinity of polar azobenzene moiety.

• Macromolecular Research
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• v.16 no.5
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• pp.434-440
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• 2008

Three-armed, star-shaped molecules containing 4-(N,N-diphenyl)amino-4'-nitroazobenzene chromophores were synthesized to study the diffraction behavior after inscribing surface relief gratings. The two molecules differed in terms of their mode of chromophore attachment to the core. In compound 5, they were bound to the core laterally through alkylene spacers, whereas the chromophores were tethered perpendicularly to the core in compound 4. Although 60 wt% of the polar azobenzene chromophores was comprised of large molecules, no aggregation behavior was observed in the absorption spectra of the thin films. The surface relief gratings were elaborated on the surface of the molecular films by the two-beam interference method. The dynamics of grating formation were studied in terms of the diffraction efficiency using two different film samples made up of two star-shaped molecules. The maximum diffraction efficiency of D-$(ENAZ)_3$, compound 4, was measured to be about 30%, which was significantly high. The mode of chromophore attachment affected the dynamic properties of the diffraction gratings.

• Bulletin of the Korean Chemical Society
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• v.20 no.9
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• pp.1010-1016
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• 1999

We synthesized the photoresponsive side chain polymers containing aminonitro azobenzene for studying the effect of temperature on photoinduced birefringence. Four different copolymers were prepared using methacrylate, α-methylstyrene, and itaconate monomer. Photoisomerization was observed under the exposure of UV light using UV-VIS absorption spectroscopy. Reorientation of polar azobenzene molecules induced optical anisotropy under a linearly polarized light at 532 nm. The change of the birefringence was observed with increasing the sample temperature under a continuous irradiation of excitation light. We could estimate the activation energy of molecular motion in thermal and photochemical mode. Besides the effect of glass transition temperature on the activation energy, we focused our interests on the effect of geometrical hindrance of polar azobenzene molecules and cooperative motion of environmental mesogenic molecules in the vicinity of polar azobenzene molecules.

• Journal of the Korean Applied Science and Technology
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• v.31 no.1
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• pp.50-58
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• 2014

A novel fullerene derivative with photoresponsive azobenzene group was designed and synthesized, and its photoresponsive properties were reported. Starting from 4-nitrophenol, compound 1, which is containing fullerene moiety connected to azobenzene group through covalent linkage was synthesized by 5 steps. All the intermediates and the final compound were characterized by $^1H$, $^{13}C$-NMR, FAB-Mass or elemental analysis. Compound 1 exhibited the expected photoresponsive behavior. Chloroform solution($10^{-5}M$) of it served to maximize the absorption at 351 nm corresponding to the trans-azobenzene chromophore. Irradiation of this solution with 365 nm light resulted in photoisomerization to cis-azobenzene, as evidenced by decrease in the absorbance at 351 nm and an increase in absorbance at 450nm. A photostationary state was reached within about 150 s. Thermal reversion to the original spectrum was observed over the course of about 6 h at room temperature in the dark. However, exposure to bright sun light for about 5 s also effect almost complete reversion to the trans-isomer. This indicates that there is no strong steric influence on the trans-cis reversible isomerization of compound 1.

• Macromolecular Research
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• v.8 no.4
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• pp.172-178
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• 2000

We synthesized polymethacrylate and polyurethane bearing a photosensitive azobenzene chromophore. Photo-induced birefringence of the thin film was observed under a linearly polarized light(λ = 532 nm). Dynamic behaviors of birefringence in two polymers were investigated in terms of the rate constants of growth and decay. An induced dichroism was observed from polarized UV-VIS absorption spectroscopy. Layers of two photosensitive polymers were used for aligning liquid crystal (LC) molecules instead of one of the rubbed polyimide layers in the conventional twisted nematic cell. For producing homogeneous alignment of a nematic LC molecule, a linearly polarized light was exposed to the films of two polymers. The stability of the LC alignment upon the linearly polarized light exposure was also studied.

• Advances in materials Research
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• v.1 no.4
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• pp.299-310
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• 2012

This article describes the synthesis of a novel N-substituted pyrrole monomer containing an azobenzene group. The 2-[N-ethyl-N-[4-[(4-nitrophenyl) azo]-phenyl] amino] ethyl-3-chloropropionate (RedII) compound was synthesized via reaction of 4-nitro-4'-[N-ethyl-N-(2-hydroxyethyl)-amino] azobenzene (RedI) and 3-chloropropionic acid. RedII was reacted with the potassium salt of pyrrole then 2-[N-ethyl-N-[4-[(nitro phenyl) azo] phenyl] amino] ethyl-N-pyrrolyl propionate (Py-RedII) was prepared. Chemical polymerization of Py-RedII and copolymerization of Py-RedII with pyrrole carried out using $FeCl_3$. Poly (2-[N-ethyl-N-[4-[(nitro phenyl) azo] phenyl] amino] ethyl-N-pyrrolyl propionate) (PPy-RedII) was characterized by UV, IR, $^1HNMR$, $^{13}CNMR$ spectroscopies. Electropolymerization of Py-RedII and electroco-polymerization of Py-RedII and pyrrole were studied using conventional three electrodes system, Ag/AgCl reference electrode, platinum counter electrode and GC disk working electrode. Scanning electron microscopy (SEM), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) were used for thermal and rheological studies. The TGA curve of PPy-RedII demonstrated a high thermal stability up to 200°C and its DSC thermogram showed two endothermic peaks at 88 and $122^{\circ}C$. The glass transition temperature of the polymer was found to be above the room temperature. Electrical conductivities of PPy-RedII and it's copolymer with pyrrole (PPy-RedII-co-Py) were studied by the four-probe method and produced conductivities of $7.5{\times}10^{-4}$ and $6.5{\times}10^{-3}Scm^{-1}$, respectively.