Young-Sun Cho

Polymer electrophosphorescent device: comparison of phosphorescent dye doped and coordinated systems

Abstract We have synthesized a new polymer, (poly(Ir(ppy)2(2-(4-vinylphenyl)pyridine))-co-vinylcarbazole)) [Ir complex copolymer], containing both carbazole and iridium(III) complex as side groups and fabricated electrophosphorescent polymer light emitting devices. The 1MLCT transition of Ir complex copolymer is almost same position and absorption intensity of 8% Ir(ppy)3 doped PVK. At a lower molar concentration of the Ir complex copolymer, the polymer exhibited emission only from the carbazole units. However, with gradual increase in the concentration of the Ir complex copolymer, emission from the Ir complex became dominant. Present results indicated the energy transfer takes place by the intermolecular energy transfer not the intramolecular energy transfer. From the PL and EL of film state, the emission maximum was observed at 512 nm, due to the radiative decay from the 3MLCT state to the ground state, confirming almost a complete energy transfer from carbazole to Ir complex. The device showed 4.4% maximum external quantum efficiency and 5.0 lm/W power efficiency and peak luminance of 12,900 cd/m2.

Hyaluronic acid and silver sulfadiazine-impregnated polyurethane foams for wound dressing application

Five different kinds of PU foam wound dressings were prepared to investigate their wound healing capability. They include (i) PU+silver sulfadiazine (AgSD), (ii) PU+alginate (Al), (iii) PU+Al+AgSD, (iv) PU+hyaluronic acid (HA), and (v) PU+HA+AgSD. Physical properties and in vitro behaviors of AgSD release and fibroblast adhesion on those dressings were evaluated. From the drug release and fibroblast adhesion studies, it was observed that PU foam impregnated with both HA and AgSD shows good drug release behavior and low adhesion of the cells. Furthermore, the HA and AgSD-containing PU foam showed excellent wound healing effect without any inflammation or yellow cluster. The wound size decreased around 77% after 1 week application of that foam dressing onto a rat skin defect.

Controlled Anionic Synthesis of Poly[2‐(3‐nitrocarbazolyl)ethyl methacrylate]

Poly[2-(3-nitrocarbazolyl)ethyl methacrylate] (poly(NCzMA)) with controlled molecular weight and narrow molecular weight distribution was successfully synthesized using (methyl methacryloyl)potassium (MMA) as a weak initiator in the presence of diethylzinc (Et2Zn) in THF at –78°C. Et2Zn acted both as an additive for the coordination with enolate anion and nitro group and as a scavenger to remove impurities. Block copolymers PMMA-block-poly(NCzMA)-block-PMMA and poly(NCzMA)-block-PS-block-poly(NCz-MA), were also synthesized quantitatively (PMMA: poly(methyl methacrylate), PS: polystyrene). The results indicate that Et2Zn can be used to synthesize the polymers of solid, nitro group-containing methacrylate monomers by anionic polymerization in THF.

Synthesis and Properties of Ruthenium-Coordinated Block Copolymers of 2-Vinylpyridine and Carbazole Derivatives

ABA triblock copolymers consisting of different carbazole-containing blocks and ruthenium complexes were designed with respect to their energy-transfer behavior. The number of 2-vinylpyridine (2VP) units in a polymer chain was tailored from 0 to 20 to observe the size effect of the metal complex as a luminophore or as a luminescence quencher. Photoluminescence and optical absorption measurements as well as the intermolecular energy transfer in the block copolymers were studied. Evidence is provided for a fast energy transfer from carbazole to the ruthenium-coordinated 2VP.

Hydrolysis and condensation of fluorine containing organosilicon

Abstract To generate sol–gel film from the hydrolysis and condensation reaction of fluorine containing organosilicon monomers, 3-trifluoromethylphenyltriethoxysilane (TFSI), 3, 5-bistrifluoromethylphenyltriethoxysilane (BTFSI) and pentafluorophenyltriethoxysilane (PFSI) were synthesized. The reactivity of each monomer was investigated by 1H-NMR spectroscopy in the presence of a confirmed concentration of hydrochloric acid, water and hexafluorobenzene. According to the integration ratio of ethanol/ethoxy peak for all monomers, the ethoxy groups were almost remained constant during some period and then disappeared very quickly. PFSI showed higher reactivity than TFSI and BTFSI at the same reaction condition. The clear film was easily fabricated by spin coating and crosslinked at 270 °C for 2 h. The cured films showed good chemical resistance and thermal stability until 398 °C. At 1.55 μm wavelength, the refractive indices and birefringences of the sol–gel films were in the range of 0.0005–0.0009 and 0.0031–0.0034, respectively, depending on feed ratio of TFSI or BTFSI and PFSI.

Preparation of Gold-Polypyrrole Core-shell Nanoparticles

Abstract The core-shell particles consisting of a nano-sized gold colloidal core and polypyrrole (Ppy) shell were simply prepared by using adsorbed cationic surfactants (cetyl pyrridinium chloride:CPC) arrays as template. The Ppy shell layers were effectively deposited under a condition where the CPC are adsorbed as bilayers on the surfaces of gold nanoparticles (Au). The Au-Ppy core-shell nanoparticles were found to be stable colloidal dispersion in aqueous media with 45 nm in diameter employed Ppy shell with 10 nm thickness.

Anionic Living Polymerization of Monomers with Photo-Electronic Properties for Control of Polymeric Nano Architectures

Abstract Block copolymers, 9-ethylcarbazolyl methacrylate (CzMA) with 3-nitro-9-ethylcarbazolyl methacrylate (NCzMA), and styrene with optically functionalized isocyanates containing disperse red 1 (DR1NCO) and (s)-(-)-2-methylbutanol (MBI), were prepared by anionic polymerization for photo-electronic materials. The living condition of CzMA was found at -78°C for 3 h with diethyl zinc and block copolymers of CzMA with NCzMA were synthesized successfully. The polymers show potential to be used as energy transfer materials in UV and PL spectra. Block copolymers of styrene with optically functionalized isocyanates were also synthesized with high yield and the polymers showed the large optical activity at 476 nm.

UV STUDY ON THE THERMAL STABILITY OF DISPERSE RED 1 FILMS INCORPORATED WITH REACTIVE SILICA

Abstract The thermal stability of thin DR1/PMMA, DR1/silica, and DRS/silica systems was studied by UV spectroscopy. DRS which can covalently bind with reactive silica was synthesized between 4-[ethyl(2-hydroxyethyl) amino]-4′-nitro azobenzene (disperse red 1, DR1) and 3-isocyanatopropyl triethoxy silane The characterization of chemicals and incorporated films were carried out by UV/VIS spectroscopy, DTA, 1H-and 13C-NMR, and FT-IR. After poling of DR1 and DRS incorporated at various temperatures, the UV absorbance decreased due to the alignment of DR1 and DRS by electric field. The second harmonic generation response was obtained by using Nd:YAG laser. The thermal stability of DRS and DRS/silica system was enhanced, compared to that of DR1 and DR1/silica system, respectively.

Nonlinear Optical Properties of Modified Dr1/Silica Films with Highly Ordered Structures

Abstract Crosslinkable organic NLO chromophore (DRS) has been prepared and chemically incorporated into silica matrices using a sol-gel process. By monitoring the decay of UV absorbance as a function of time and temperatures, a number of electrically poled DRS/silica matrice system has been investigated to elucidate the relaxation behaviors of the oriented organic chromophore by the poling. The value of the second order NLO coefficient d33 was 47 pm/V for the DRS/silica matrice films with 0.4 μm thickness. In addition, from the result of dramatic decreasing of UV absorbance after poling, it is speculated that the DRS may act as a liquid crystalline mesogenic groups and effectively oriented by the poling at the phase (nematic) transition temperature (80°C) and locked in by the crosslinking. The crosslinking reactions between silica matrices and DRS chromophores have been proved using 29Si solid NMR measurement.

Enhanced Adhesion of Deposited Polypyrrole Ultra-Thin Films Through Self-Assembled Polymeric Monolayers

Abstract A novel method for the deposition of polypyrrole (PPy) thin films on a metal oxide surface using self-assembled polyethylene glyeol (PEG) monolayers as reaction media has been developed. This method lends to increased adhesion of the deposited PPy films to the substrates and an increase in its electrical conductivity. The procedure consists of several simple steps. First, the surface of glass substrate is functionalized with the isocyanate group. Then, a PEG monolayer is formed on the surface through the reaction of its hydroxy group with the isocyano group. Finally, a polypyrrole film is grown in the self-assembled PEG monolayer by adding oxidant. The resulting PPy thin films were characterized by measuring the electrical conductivity, adhesion, and surface morphology. It was found that the deposited PPy films show higher conductivities (13 s/cm) and superior adhesion compared to simply deposited PPy films.