Byoung-Ki Cho

Dankook University, Eidō, Chungcheongbuk-do, South Korea

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Publications (67)332.98 Total impact

  • Source
    Kyuwon Han · Byoung-Ki Cho
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    ABSTRACT: In this paper, we report the emission properties of two luminogens, which possess an identical extended tetraphenylethylene (TPE) aromatic core, but different hydrophobic dodecyl (1) and hydrophilic di(ethylene oxide) (2) peripheral chains. In comparison to the dilute chloroform solutions (0.1 μM), the emission of the chloroform solutions (10 μM) was red-shifted, which indicates an intermolecular interaction with increasing concentration. To investigate the chain-dependent emission behavior of 1 and 2, polar methanol and nonpolar n-hexane were employed as two poor solvents. As a consequence, upon adding each poor solvent, the emission properties were predominantly dependent upon the solubility between the peripheral chain and the mixture solvent (chloroform/poor solvent). Despite the identical aromatic chromophore, the emission could be guided by the nature of the attached peripheral chains. Upon increasing the fraction of the poor solvent for a peripheral chain, the crystallization of the TPE-based aromatic cores occurred, which produced a bright bluish emission. Scanning electron microscopy observation could confirm the ordered morphologies of the bluish aggregates. By comparing the integral values of the aromatic segments in the 1H-NMR spectra with increasing the poor solvents, it can be said that the crystallization is initiated by the retardation of the conformational motions of the TPE aromatic ring, not the whole aromatic segment. In addition, by replacing chloroform with water-mixable tetrahydrofuran, two polar solvents, i.e., water and methanol, could be distinguished using the two emission color codes of 1 and 2. The molecular approach (the simple variation of the peripheral chain) in this study proved an alternative way to tune the solution emission of the identical chromophores.
    Preview · Article · Jan 2015 · RSC Advances
  • Soyoung Park · Byoung-Ki Cho
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    ABSTRACT: In this paper, we report thermally induced intercolumnar transitions of C3-symmetric liquid crystals (LCs) bearing a triazole-based propeller-like aromatic mesogen. Since the constituting aromatic rings are conjugated through rotatable single bonds, the mesogenic shape is tuneable depending on the degree of the conformational motion. Molecule 1 with ninefold octyl peripheries shows a hexagonal columnar liquid crystalline phase transition from ordered mesogenic stacking to disordered mesogenic stacking upon heating. On the other hand, molecule 2 with sixfold octyl peripheries displays a helical hexagonal columnar phase with P6/mmm space group at ambient temperature as well as the ordered and disordered hexagonal columnar phases at higher temperatures. The intracolumnar helical order can be understood by an interdigitated stacking of the propeller-like mesogens along the columnar axis and the optimized space-filling. Notably, all the intercolumnar phase transformations in this study are revealed as second-order transitions. The thermodynamic nature agrees well with the fact that the conformational motions of the C3-symmetric aromatic mesogen change abruptly with each columnar transition.
    No preview · Article · Oct 2014 · Soft Matter
  • Inhye Kim · Na-Eun Lee · Yoo-Jeong Jeong · YH Chung · Byoung-Ki Cho · Eunji Lee
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    ABSTRACT: We herein report the molecular assemblies of the click-derived amphiphiles bearing a triazole-based aromatic block and their heavy metal ion conjugates in a 100% water environment. The length and conformational rigidity of the aromatic block affected the aqueous assemblies of amphiphiles. In particular, the amphiphile 2N based on the rigid naphthalene unit formed a vesicular nanostructure above the CMC. Interestingly, the assembly power of the amphiphiles could be enhanced by Hg2+-capturing of the triazolyl units. Amphiphiles 2 and 2N formed micellar and vesicular aggregates with a fluorescence turn-off response, even below their CMCs, respectively, upon the addition of Hg2+. These aqueous morphologies were determined by the stoichiometry of the amphiphile-Hg2+ complexes which affects the interfacial curvature between hydrophilic and hydrophobic parts in the nanoassemblies. Therefore, the metal-amphiphile conjugates in this study would provide a useful and simple strategy for the detection of toxic heavy metals in aqueous medium. In addition, the resultant vesicular hybrids induced by the response to specific metal ion would open up the development of novel functional nanovehicles in response to specific chemical species.
    No preview · Article · Sep 2014 · Chemical Communications
  • Source
    Minjoo Noh · Byoung-Ki Cho
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    ABSTRACT: In this paper, we report the thermal, morphological, lower critical solution temperature (LCST), and ion-conducting properties of electrolytes based on a dendron-coil-dendron block copolymer (BCP) and ionic liquids (ILs). The BCP consists of ionophilic poly(ethylene oxide) middle and ionophobic dendron ends with crystalline octadecyl peripheries. The two ILs that were employed, 1,2-dimethyl-3-propylimidazolium tetrafluoroborate ([PMMIM][BF4]) and 1-buty-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), had identical molecular weights but different molecular structures in the imidazolyl cation. The electrolyte (1) with [PMMIM][BF4] exhibited crystalline lamellar and disordered micellar phases as a function of temperature. On the other hand, the electrolyte (2) with [BMIM][BF4] showed an additional ordered hexagonal columnar liquid crystalline (LC) phase in between the crystalline lamellar and the disordered micellar phases. Infrared absorption studies suggest that the induction of the ordered LC phase is attributed to the strong hydrogen-bondings between PEO and [BMIM]. Furthermore, it was found that the electrolyte (2) suddenly started to become turbid near the order-to-disorder transition temperature (TODT). This indicates that the LCST of 2 is identical to the TODT, above which liquid-liquid separation occurred gradually. The ionic conductivity curve of 1 increased continuously as the temperature increased. In contrast, 2 displayed a sudden drop in conductivity upon changing from the crystalline lamellar to the columnar phase, which was due to the variation of the ionophilic domain dimensionality from two to one. The calculated activation energy for ionic conduction in each phase was revealed to be affected by the translational motion and polarity of the ion-carrying medium.
    Preview · Article · Aug 2014 · RSC Advances
  • Kyuwon Han · Byoung-Ki Cho
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    ABSTRACT: Novel hexacatenar molecules based on a 1,2,3-triazole-extended aromatic rod self-assemble into crystalline monoclinic and liquid crystalline hexagonal columnar structures depending on temperature. The phase transition may involve a conformational change from an anisotropic transoid to a half-disk cisoid conformer upon melting. In a hexacatenar molecule with sixfold octyl chains, the crystal-to-LC transition accompanies a photoluminescence color change from sky blue to dark blue, which is attributed to the formation of higher-order aggregates in the crystalline state.
    No preview · Article · Aug 2014 · Soft Matter
  • Soyoung Park · Mi-Hee Ryu · Tae Joo Shin · Byoung-Ki Cho
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    ABSTRACT: In this paper, we report a C3-symmetric liquid crystal (LC) with sixfold alkyl peripheries exhibiting an unusual smectic E-like organization in the LC state. Based on conformational considerations, the smectic assembly is attributed to the formation of an endo-type Y conformer of asymmetric triazolyl and benzylic groups that cannot be accessed in other C3-symmetric molecules exclusively showing columnar assemblies. The Y conformers form a two-dimensional oblique lattice in the aromatic layers of the ordered smectic phase. In addition, the Y-shaped molecule in the smectic phases can change into a circular shape by the 1 : 1 hydrogen-bonding interaction with a gallic acid derivative, which leads to a hexagonal columnar LC phase. The triazole-based LC design concept proves the smectic LC assembly in the C3-symmetric system, and provides the supramolecular manipulation of LC morphologies.
    No preview · Article · Jun 2014 · Soft Matter
  • Source
    Byoung-Kwan Lee · Jun Hee Yoon · Sangwoon Yoon · Byoung-Ki Cho
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    ABSTRACT: A bent-shape triazolyl derivative was synthesized via click chemistry, and its photophysical property was investigated in various solvents. In contrast to the invisible ultraviolet emission of other solutions, the chloroform solution exhibited a blue light emission at 460 nm. Furthermore, the blue fluorescence intensified as the UV exposure time at 365 nm increased. On the basis of -NMR, pH paper, and acid-addition studies, we confirmed that chloroform was decomposed into HCl with the aid of the triazolyl derivative. The density functional theory calculations suggested that the eye-detectable blue fluorescence was attributed to an intramolecular charge transfer process of the protonated triazolyl derivative in the chloroform solution.
    Preview · Article · Jan 2014 · Bulletin- Korean Chemical Society
  • Byoung-Ki Cho
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    ABSTRACT: This review introduces research work in the area of organic liquid crystalline (LC) electrolytes consisting of ionophilic and ionophobic groups. I discuss the LC phase behavior and morphology-dependent ion conduction of organic electrolyte systems based upon (i) coil-coil block copolymers (BCP), (ii) dendritic BCPs, (iii) mini-dendron-based liquid crystals, and (iv) rod-type liquid crystals. As a way to improve ionic conductivity and mechanical strength, the self-assembling approach of each LC system and other processes including macroscopic alignment techniques and post-polymerizations are described.
    No preview · Article · Jan 2014 · RSC Advances
  • Byoung-Ki Cho · Seung-Hyun Kim
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    ABSTRACT: We prepared three discotic liquid crystals (DLCs) based on a triphenylene (TP) disc functionalized with twelve alkyl peripheries. The synthesis of the discogens was performed by a click reaction using Cu(OAc)2 as the catalyst, with six triazolyl groups connecting the TP core with twelve alkyl chains. According to thermal data from differential scanning calorimetry (DSC), discogen , which has the shortest hexyl peripheries, exhibited two LC phases, and and , with decyl and tetradecyl peripheries, respectively, displayed three LC phases as a function of the temperature. Structural analyses using small- and wide-angle X-ray scattering (SAXS and WAXS) techniques revealed ordered and disordered hexagonal columnar LC phases in all the discogens. On the other hand, an unconventional micellar phase with P42/mnm symmetry consisting of thirty micelles was found only in and , when the temperature increased. The thermally induced transformation from the columnar to the micellar phase can be explained by increased chain entropy at higher temperatures. The complex micellar packing in the noncubic phase is attributed to the softness of the DLC micelles because the micellar corona consists of flexible alkyl chains. The discogen design concept in this study (i.e., the introduction of multibranched alkyl peripheries to the discotic mesogens via click chemistry) resulted in unconventional columnar-to-micellar transformation in conventional TP DLCs.
    No preview · Article · Dec 2013 · Soft Matter

  • No preview · Article · Dec 2013 · Macromolecular Research
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    ABSTRACT: The amphiphilic block codendrimer self-assembled into supramolecular vesicles with a bilayer membrane in both hydrophilic and hydrophobic solvents. Surface-modified quantum dots (QDs) were successfully entrapped within the wall of vesicles through a simple self-assembly process without any structural disruption.
    No preview · Article · May 2013 · Chemical Communications
  • Sujin Choi · Byoung-Ki Cho
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    ABSTRACT: We synthesized three dendron–coil-dendron block copolymers consisting of ionophilic poly(ethylene oxide) (PEO) coils and mesogenic dendrons with four octadecyl peripheries via stepwise click reactions. The obtained polymers were doped with lithium triflate, whose concentration per ethylene oxide unit was 0.05. As characterized by optical polarized microscopy (POM) and X-ray scattering techniques, polymer 1 with the shortest PEO coil (Mn = 2000 g mol−1) did not show the liquid crystalline (LC) phase, while its ionic sample (1-Li+) exhibited a hexagonal columnar LC phase. On the other hand, 2 and 3 (with PEOs of Mn = 4000 and 8000 g mol−1, respectively) displayed identical LC morphologies to 2-Li+ and 3-Li+, respectively, although the phase transition temperatures increased upon salt doping. For 2 and 2-Li+, gyroid and lamellar LC phases were observed with increasing temperature, while 3 and 3-Li+ showed only a lamellar LC phase. The observed ion-transporting behavior was strongly dependent upon the connectivity of ion-conducting domain structures. The investigation of the morphology–conductivity correlation using a normalized conductivity (σ* = σ/f, where σ and f are the original conductivity and the PEO volume fraction) indicated that the 3-D gyroid LC phase showed the highest value, while the lowest conductivity was found in the 1-D columnar structure at identical temperatures. Additionally, the gyroid to lamellar phase transition temperature of 2-Li+ could be determined by the σ*, which was consistent with the X-ray data. Consequently, the results can be explained by the fact that the ionic pathway becomes complicated when going from higher to lower dimensional structures in polygrain samples.
    No preview · Article · Mar 2013 · Soft Matter
  • Source
    Jie Song · Byoung-Ki Cho

    Preview · Article · Jan 2013 · Bulletin- Korean Chemical Society
  • Jie Song · Eunji Lee · Byoung-Ki Cho
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    ABSTRACT: A well-defined (PEO-PS)2-PLA miktoarm terpolymer (1) was synthesized by stepwise click reactions of individually prepared poly(ethylene oxide) (PEO), polystyrene (PS, polymerized by atom transfer radical polymerization), and polylactide (PLA, polymerized by ring-opening polymerization) blocks. As characterized by differential scanning calorimetry and small-angle X-ray scattering techniques, the terpolymer self-assembled into a hexagonal columnar structure consisting of PLA/PEO cylindrical cores surrounded by PS chains. In contrast, the ion-doped sample (1-Li+) with lithium concentration per ethylene oxide = 0.2 exhibited a three-phase lamellar structure, which was attributed to the microphase separation between PEO and PLA blocks and to the conformational stabilization of the longest PLA chain. The two-phase columnar morphology before the ion doping was used to prepare a nanoporous material. PLA chains in the cylindrical core region were hydrolyzed by sodium hydroxide, producing nanopores with a pore diameter of about 14 nm. The resulted nanoporous material sank to the bottom in water, because of water-compatible PEO chains on the walls. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
    No preview · Article · Jan 2013 · Journal of Polymer Science Part A Polymer Chemistry
  • Jie Song · Byoung-Ki Cho
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    ABSTRACT: In this study, we investigated the functionality- and size-dependent differentiation capability of bulk nanoporous polystyrene (PS) materials in aqueous environments. A three-arm star block copolymer (consisting of dibranched PS and linear polylactide (PLA) blocks) was employed to prepare PS nanochannels with the average pore diameter of 14.2 nm. Due to the ester group at the junction of the PS and PLA blocks, a negatively charged carboxylate group could be placed as the wall functional group automatically after the PLA etching. Based on specific electrostatic interactions, the bulk PS channels with the carboxylated wall could selectively capture a water-soluble cationic dye (rhodamine 6G) in the aqueous and methanolic solutions. Furthermore, the well-defined porous PS displayed excellent size-dependent selectivity, which was proved by a fluorescence quenching experiment using differently sized gold nanoparticles (AuNPs). Rhodamine 6G dyes on the pore wall were effectively quenched by 2 nm AuNPs. In contrast, the 16 nm AuNPs (larger than the pore diameter) did not affect the brightness of the rhodamine 6G-loaded PS.
    No preview · Article · Nov 2012 · ACS Macro Letters
  • Jie Song · Byoung-Ki Cho
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    ABSTRACT: We reported a synthetic protocol of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) copolymers via dehydrobromination and click coupling reactions. The PS block (acetylene-PS) was prepared by anionic polymerization and end-functionalized with an acetylene group. The other PMMA block was synthesized by an atom transfer radical polymerization (ATRP) of MMA using an azido-initiator. It was found, unexpectedly, that the click reaction of acetylene-PS and the bromide-ended PMMA using Cu(I)Br yielded a byproduct with double the molecular weight of the product (PS-b-PMMA). This was attributed to the coupling of the bromide ends of block copolymers. This problem could be avoided by a dehydrobromination of the PMMA block into the olefin end (azido-PMMA-ene) using tetra-n-butylammonium fluoride (TBAF) at room temperature. Due to the mild dehydrobromination condition and the weak basicity of TBAF, no hydrolysis of PMMA esters occurred. After the click coupling of acetylene-PS and azido-PMMA-ene, the excess PS was removed by further click reaction using insoluble PS resins surface-functionalized with azide groups.
    No preview · Article · Oct 2012 · Macromolecular Research
  • Jie Song · Byoung-Ki Cho
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    ABSTRACT: A micellar cubic LC phase consisting of a hydrophilic matrix exhibited enhanced ionic transport and mechanical properties without macroscopic orientation, which are attributed to the non-tortuous ionic transport and highly symmetric cubic lattice, respectively.
    No preview · Article · May 2012 · Chemical Communications
  • Source
    Jung-Guk Ha · Jie Song · Jeong-Kyu Lee · Byoung-Ki Cho · Wang-Cheol Zin
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    ABSTRACT: In contrast to the known perpendicular ordering of conventional PS-b-PLA thin films, branched (PS)(2)-b-PLA thin films showed two different parallel orientations whose locations are strongly dependent upon film thickness.
    Preview · Article · Apr 2012 · Chemical Communications
  • Byoung-Ki Cho
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    ABSTRACT: This paper reviews our recent research with regard to bulk self-assemblers based on well-defined branched building blocks. Branched molecules/polymers have been known to show different physical properties from conventional linear-shaped polymers. As well as thermal and solution properties, structural modification into branched building blocks also has a significant influence on self-assembling behavior in the bulk states, including solid and liquid crystalline (LC) phases. As a branched component, dendrons/dendrimers with well-defined structures can be ideal candidates for the construction of advanced self-assemblers. Recently, we worked on new assembling systems such as dendron-coils, block codendrimers and discotic LC molecules. In the design, we used aliphatic polyether dendrons in most cases and poly(benzyl ether) dendrons in part. Their bulk assembling and thermal properties were found to be distinct from conventional linear block copolymers and they were dependent upon their chain architectures. To self-assemble into ordered nanostructures, the hybrid assembers were designed to have incompatible blocks, for example, hydrophilic and hydrophobic parts. Furthermore, in some cases an ionic complexation was carried out to maximize the immiscibility between the two different blocks. This review describes the molecular manipulations to engineer the nanoassemblies in bulk and also the ionic transportation properties depending on the assembling morphology.
    No preview · Article · Mar 2012 · Polymer Journal
  • Jie Song · Byoung-Ki Cho
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    ABSTRACT: A series of self-assembling dendron-coil block copolymers with well-defined molecular structures were prepared via a divergent method. The hydrophilic and hydrophobic blocks are composed of PEO-like dendrons and poly(ethylene-alt-propylene) (PEP) linear coils, respectively. A dendron-coil, 2G-2400 (2G and 2400 indicate the dendron generation and PEP molecular weight, respectively), showed a melting transition of the peripheral PEO chains. In contrast, the dendron-coils containing the 3rd generation dendron did not show any melting transition because of the plasticization effect of the tri(ethylene oxide) branches. Due to the strong immiscibility between the PEO-like dendron and PEP blocks, diverse microphase-separated morphologies were observed. 2G-2400 displayed a lamellar mesophase with an interdigitated dendron packing structure. For the larger 3rd generation dendron series, A15 micellar cubic (Pm3n space group), hexagonal columnar, and lamellar morphologies were revealed depending on the PEP coil length and/or temperature. For the columnar mesophases, the molecular wedge angles (α) were calculated to be 46.8° and 34.6° for 3G-2400 and 3G-3400, respectively. This suggests that the longer PEP coil of 3G-3400 is conformationally more deformed in the columnar structure. As a consequence, the columnar phase was transformed into an interdigitated lamellar structure as the temperature increased. This order to order transition is a reversal of the well-known phase sequence of linear block copolymers. This unusual morphological behavior is mainly attributed to the unique molecular arrangement associated with non-conventional dendron-coil chain architecture.
    No preview · Article · Feb 2012 · Soft Matter

Publication Stats

1k Citations
332.98 Total Impact Points


  • 2005-2015
    • Dankook University
      • Department of Chemistry
      Eidō, Chungcheongbuk-do, South Korea
  • 1998-2007
    • Yonsei University
      • Department of Chemistry
      Sŏul, Seoul, South Korea
  • 2004-2005
    • Cornell University
      • • Department of Physics
      • • Department of Materials Science and Engineering
      Итак, New York, United States