Bong-Keun So

Novel bent-shaped liquid crystalline compounds: 1. Synthesis and structure analysis of dimesogenic compounds with azo units

Abstract A new series of bent-shaped liquid crystalline compounds (2An), which were composed of two identical mesogens (azobenzene-type), terminal alkyloxy chains (n=6, 8, 10, 12) and 2-hydroxy-1,3-dioxypropylene as central linking unit, have been prepared. Their mesomorphic properties were characterized by polarized light microscopy, differential thermal analysis, and X-ray diffraction (XRD). For 2An series, n=8, 10 and 12 compounds showed enantiotropic SmC phase, but n=6 compound did not show liquid crystal phase, as was confirmed by the XRD patterns.

Novel bent-shaped liquid crystalline compounds II. Synthesis and properties of the 1,3-bis{4-[4-(4-alkyloxybenzoyloxy)benzylidene]aminophenoxy}propan-2-ols

A series of new symmetric dimer compounds was synthesized, constaining 2-hydroxy-1,3-dioxypropylene as the central linkage and terminal alkyl chains with different lengths. The chemical structures of the liquid crystal dimers (2ES-n) were examined by FTIR and 1H NMR spectroscopy. Their mesomorphism, thermodynamic properties and optical textures were investigated by differential scanning calorimetry, polarizing optical microscope and X-ray diffraction. For homologues with terminal propyloxy and butyloxy chains, no liquid crystalline phase was observed. Homologues with pentyloxy and hexyloxy terminal chains showed nematic phases, while those with heptyloxy, octyloxy, nonyloxy and decyloxy terminal chains displayed nematic phases and smectic phases. The results confirmed that the liquid crystalline phase changes from nematic to smectic as the terminal chain length increases.

Thermotropic Liquid Crystalline Dimers with Varying Alkoxy Terminal Chain Length

We have design and synthesized of homologous Series I dimers and to study the effect of molecular structure variation and change in alkoxy terminal chain length (n = 6, 7, 8) on mesomorphic properties of liquid crystals. Explore further understanding of the structure-property relationship of liquid crystal homologous Seriesl dimers having varying alkoxy terminal chain length. It was found that the decrease in crystalline phase, smectic C and nematic phase transition temperatures with increasing terminal alkoxy chain length. The molecular structures of the Seriesl dimer were characterized by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. Their mesomorphic properties were investigated by differential scannning calorimetry (DSC) and on the hot-stage of a polarizing microscope (POM).

Multibranched and dendritic organic materials with high two-photon absorption activity

A three-dimensional micro-object was fabricated by two-photon initiated photopolymerization (TPIP) of soft-resin with the efficient two-photon absorbing multi-branched chromophore, EPS-3arm, which possesses high two-photon absorption cross-section of 5.21×10-47 cm4s/photons at 700 nm. The structural stability of the fabricated micro-objects could be achieved with aid of sol-gel process. The two-photon absorbing stilbazolium-cored dendrimer was also synthesized. The stillbazolium chromophore was covalently linked with the dendrimer chains so as to restrict free conformation motion. The hindered molecular twisting motion of the stilbazolium dye within the dendrimer is responsible for 5 to 16 times of enhancement in fluorescence emission along with the increased emission lifetime. The steady-state and time-resolved fluorescence emission study of the solid-state film indicate an efficient site-isolation and restriction of conformation motion of the active two-photon chromophore.

Rigidity Dependence of Alignment and Relaxation in Main-Chain Nonlinear Optical Polymers Measured by Optical and Electrical Method

Abstract The dynamics of two main-chain nonlinear optical polymers, PA-PS and PA-MS, was studied at various temperatures below Tg. In the characterization, both the photo-induced isomerization method and second harmonic generation were employed. In the case of non-polar alignment by the linearly polarized UV light, the main-chain of PA-PS polymer was found well re-aligned but the main-chain of PA-MS polymer was not, because of the high rigidity. In the case of polar alignment by in-situ corona poling technique, double exponential functions fit well to the data of both PA-PS and PA-MS polymer relaxation data at all the temperature range.

Liquid crystal properties of dimers having two identical terminal units and a central oxyethylene spacers

ABSTRACT Liquid crystal compounds are an important state of matter both scientifically and technologically. So we have prepared HSEO-n(n = 1,2,3,4) series shown below. In this study, in orde to acquire further understanding of the structure-property relationship of HSEO-n series, the chemical structure of the intermediates and the final products HSEO-n series was studied by fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy and the liquid crystal properties and optical textures of the HSEO-n series were characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM).

Efficiently Site-Isolated Two-Photon Absorbing Dendrimer with Stilbazolium Chromophore

To prevent the chromophore aggregation, a dendritic stilbazolium salt-type chromophore was synthesized via base-catalyzed coupling reaction of trihydroxy-functionalized tetraphenylborate stilbazolium salt core with appropriate peripheral Fréchet-type dendrons G3-benzyl bromide. The casted solid film of the resulting two-photon absorbing dendrimer showed high fIuorescence efficiency and optical power limiting activity which were not observed from the bare chromophore without dendrons. This result is attributed to the site isolation effect of its dendritic structure. By introducing this chromophore we have successfully fabricated micropatterns with high resolution by two-photon polymerization.

Poling and Relaxation Dynamics of a Nonlinear Optical Polyimide: Temperature-Dependent SHG Study

Abstract The temperature dependence of second harmonic generation efficiency have been studied to investigate the poling and relaxation dynamics of polyamic acid carrying two end-on attached chromophores of DR1 and DANS. We interpreted the experimental results with the free volume model and thermal orientation fluctuation of structural components such as the nonlinear optical chromophores and main chains.