Woong Sang Jahng

Synthesis and characterization of a new photoconducting poly(siloxane) having pendant diphenylhydrazone for photorefractive applications

A new photoconducting polymer, diphenyl hydrazone-substituted polysiloxane, was successfully synthesized by the hydrosilylation method and characterized by FT-IR,1H-NMR, and29Si-NMR spectroscopy. The glass transition temperature (Tg) of the polysiloxane having pendant diphenyl hydrazone was ca. 62 °C, which enabled a component of a low-Tg photorefractive material to be prepared without the addition of any plasticizers. This polysiloxane, with 1 wt% of C60 dopant, showed a high photoconductivity (2.8×10−12 S/cm at 70 V/μm) at 633 nm, which is necessary for fast build-up of the space-charge field. A photorefractive composite was prepared by adding a nonlinear optical chromophore, 2-{3-[2-(dibutylamino)-1-ethenyl]-5,5-dimethyl-2-cyclohexenylidene} malononitrile, into the photoconducting polysiloxane together with C60. This composite shows a large orientation birefringence (Δn=2.6×10−3 at 50 V/μm) and a high diffraction efficiency of 81% at an electric field of 40 V/μm.

Optimal synthetic design of second-order nonlinear optical material with good temporal stability

Abstract Second-order nonlinear optical copolymers containing p-hydroxyphenyl maleimide or 4-cinnamoyloxy-phenylmaleimide as a comonomer were newly synthesized. For improving the temporal stability, we adopted the crosslink reaction thermally and photochemically. Second-order nonlinear optical properties of the poled/cured films were investigated in terms of the second harmonic generation (SHG) and linear electro-optic (EO) coefficient measurement. SHG coefficient, d33 was found to be 14 pm/V at the fundamental wavelength of 1064 nm and EO coefficient, r33 was found to be 25–30 pm/V at 633 nm wavelength in two different crosslinked structures. To prevent the orientational relaxation of poled polymer, thermal crosslink reaction was induced using diisocyanate as a crosslinker between the side chains themselves. Another photo-crosslink was induced exposing the film at 257 nm wavelength during poling. Temporal stabilities of second-order NLO coefficients of crosslinked polymer systems were proved much better ...

Nonlinear optical polymers with novel benzoxazole chromophores: III. Synthesis and characterization of self-crosslinkable glycidyl methacrylate copolymers

Self-crosslinkable nonlinear optical copolymers (PGBz) were synthesized by radical copolymerization of vinyl monomer containing benzoxazole chromophore and glycidyl methacrylate as a comonomer. The thermal properties of these copolymers were compared to the corresponding copolymers (PGSt) containing stilbene chromophores. It was found that both the PGBz and PGSt copolymers were amorphous and fairly soluble in chlorinated solvents such as trichloroethane and tetrachloroethane. The glass transition temperatures of the copolymers were in the range of 117–134°C depending on the contents of benzoxazole chromophores. From the results of thermogravimetric analysis before and after heat treatment, the thermal stability of PGBz copolymers was improved after heat treatment due to crosslinked polymer networks. The crosslinked PGBz had a better thermal stability than crosslinked PGSt. The nonlinear optical coefficient (d33) and electro–optical coefficient (r33) of PGBz was 63.4 pm/V (at 1064 nm) and 7.8 pm/V (1.3 μm), respectively.

Nonlinear Optical Polymers with Novel Benzoxazole Chromophores. 1. PMMA Copolymers with Good Thermal and Temporal Stability

Abstract New copolymers (PMBz) from the benzoxazole-based vinyl monomer and methylmethacrylate as a comonomer, were synthesized for an improvement of thermal stability of second-order nonlinear optical activity. The thermal stability of the chromophores in PMBz copolymers monitored by IR and UV-visible spectroscopy was much better than in PMSt copolymer bearing general pendant stilbene units. The electro-optic coefficient r33 of the poled PMBz film exhibited as large as 45 pm/V at 632 nm of He-Ne laser. Thermal relaxation behavior of the poled PMBz films at 100[ddot]C showed that the PMBz having more rigid benzoxazole structure had better temporal stability of r33 compared to the general stilbene structure.

Organically modified sol-gel materials for second-order nonlinear optics

Abstract Second-order nonlinear optical sol-gel materials containing a nonlinear optically active chromophore in the side chain were synthesized. The chromophore was covalently bonded to the silicon oxide network. Second-order nonlinear optical properties of the sol-gel films were investigated in terms of the second harmonic generation (SHG) and linear electro-optic (EO) coefficient measurement. The SHG coefficient, d 33 was found to be 20–44 pm/V at the fundamental wavelength of 1064 nm and the EO coefficient, r 33 was found to be 67–113 pm/V at 633 nm.

Nonlinear optical polymers with novel benzoxazole chromophores II. Synthesis of polyurethanes with good thermal stability

Novel diol monomer having a π-conjugated benzoxazole ring, 2-(4-nitrophenyl)-6-[N,N-bis(2-hydroxyethyl)amino]benzoxazole was successfully synthesized to improve the thermally stability of nonlinear optical chromophores. Several polyurethanes bearing pendant benzoxazole chromophores were obtained by polyaddition of the diol to various aromatic diisocyanates. The thermal stability of these polyurethanes were monitored by thetrnogravimetry and IR spectroscopy, and compared with other polyurethanes having general pendant azo chromophores. The poled polyurethane films exhibited large and stable second-order nonlinear optical properties.

Highly Efficient Photorefractive System Based on Carbazole-Substituted Poly(Siloxane)

Abstract Photorefractive polymer composite was prepared with carbazole-substituted poly(siloxane) as a host polymer, NLO chromophore and 2,4,7-trinitro-9-fluorenone as a sensitizer. This composite exhibited excellent photorefractive property. The gain coefficient determined by 2-beam coupling measurement was 250 cm −1 at 80 V/μm. And the composite was very stable toward phase separation.

Synthesis and Characterization of Functionalized Sol-Gel Materials for Electro-Optical Application

Abstract We simply synthesized the triethoxysilane bearing the second-order nonlinear optical(NLO) active chromophore in the side chain. In order to improve the poor temporal stability of second-order NLO effect, we introduced the thermal crosslink between the side chain themselves. We prepared two different silane solutions; one is composed of triethoxysilane with NLO chromophore (SGDR1) only. The other consists of SGDR1 and 3-glycidoxypropyl trimethoxysilane. Thermal crosslink formation was traced with in-situ infrared spectroscopy. We achieved much improvement of the temporal stability of second-order NLO effect utilizing this crosslinked composite system.