Yong-Rok Kim

Novel synthesis of organic nanowires and their optical propertiesElectronic supplementary information (ESI) available: experimental section and Figs. S1 and S2. See http://www.rsc.org/suppdata/cc/b1/b109881k/

Aligned nanowires of organic luminescent material were prepared by introducing the organic luminants into nanochannels of variable size in an anodic aluminum oxide (AAO) membrane, and the emission spectra from these nanowire arrays exhibited novel size-dependent luminescent properties.

Photosensitizer and vancomycin-conjugated novel multifunctional magnetic particles as photoinactivation agents for selective killing of pathogenic bacteria

Novel multifunctional magnetic particles (MMPs) conjugated with photosensitizer and vancomycin were fabricated by surface modification of Fe(3)O(4) particles. The capacities to target, capture and inactivate pathogenic bacteria and good biocompatibility suggest that the MMPs have great potentials as photodynamic inactivation agents for serious bacterial contamination.

Emission characteristics of CdS nanoparticles induced by confinement within MCM-41 nanotubes

Nanosize CdS particles confined in siliceous MCM-41 channels were prepared by using reversed micelles as an insertion carrier. As-made CdS in MCM-41 host shows photoluminescence (PL) signals from both band-edge and surface defect state recombination. Calcinated CdS in the host, however, presents relatively suppressed surface defect state emission compared with band-edge emission. Such emission characteristics after calcination is ascribed to the reduced probability of recombination through deeply trapped surface defect states compared with direct excitonic recombination, which is possibly due to surface capping of the CdS nanoparticles by the host nanochannels.

CoFe2O4 nanostructures with high coercivity

Nanometer-sized ferrite magnetic materials are the subject of intense research interest due to their potential applications in high-density magnetic information storage. One of the most explored ferrite materials is the cobalt ferrite (CoFe2O4). We have synthesized cobalt ferrite nanowires using cobalt ferrite nanoparticles in a porous anodic alumina template (AAT). The process of embedding ferrimagnetic particles into the pores was assisted by the magnetic field of a permanent magnet placed in vacuum directly under the substrate. Particles synthesized in the template were subsequently annealed at 600°C for 2h in Ar gas forming arrays of cobalt ferrite nanowires inside the AAT. The morphology of the ferrite before and after annealing was observed using a field-emission scanning electron microscope. The crystallographic structure of the nanowires was analyzed using x-ray diffraction and transmission electron microscopy. The magnetization was measured by a superconducting quantum interference device. The co...

Synthesis of highly magnetic graphite-encapsulated FeCo nanoparticles using a hydrothermal process

The graphite encapsulation of metal alloy magnetic nanoparticles has attracted attention for biological applications because of the high magnetization of the encapsulated particles. However, most of the synthetic methods have limitations in terms of scalability and economics because of the demanding synthetic conditions and low yields. Here, we show that well controlled graphite-encapsulated FeCo core-shell nanoparticles can be synthesized by a hydrothermal method, simply by mixing Fe/Co with sucrose as a carbon source. Various Fe/Co metal ratios were used to determine the compositional dependence of the saturation magnetization and relaxivity coefficient. Transmission electron microscopy indicated that the particle sizes were 7 nm. In order to test the capability of graphite-encapsulated FeCo nanoparticles as magnetic resonance imaging (MRI) contrast agents, these nanoparticles were solubilized in water by the nonspecific physical adsorption of sodium dodecylbenzene sulfonate.

Polymer–metal complex micelles for the combination of sustained drug releasing and photodynamic therapy

Polymer–metal complex micelles (PMCMs) containing cisplatin (cis-dichlorodiammineplatinum(II), CDDP), an anticancer drug, were prepared by a coordination bond of CDDP to dendrimer phthalocyanine (DPc) and poly(ethylene glycol)-block-poly(L-aspartic acid) (PEG-PLAn; molecular weight of PEG segment = 12 000 g mol−1; polymerization degrees of aspartic acid segment n = 68, 96). Transmission electron microscopy (TEM) and laser light scattering (LLS) exhibited formation of unimodal PMCM68 and PMCM96 with average sizes of 108 and 135 nm, respectively. PMCMs were very stable in 10 mM phosphate buffer solution (PBS) without NaCl to maintain their shape and size over a month. However, PMCMs slowly released CDDP when they were incubated in physiological saline PBS solution at 37 °C. Upon laser light irradiation, generation of singlet oxygen was detected by photo-luminescence observation. The PMCMs would be effective nano-devices for anticancer drug carriers with sustained drug release and photodynamic therapy (PDT).

Surface plasmon enhanced photoconductance and single electron effects in mesoporous titania nanofibers loaded with gold nanoparticles

We have synthesized mesoporous TiO2 nanofibers loaded with Au nanoparticles (MTNF-Au) and fabricated single nanofiber-based devices. MTNF-Au devices exhibited surface plasmon enhanced photoconductance under visible light, whereas MTNF devices without Au nanoparticles did not. Moreover, Coulomb oscillations were observed at 4.2 K in MTNF-Au devices, indicating that Au nanoparticles embedded in MTNF-Au played a role of Coulomb islands. These results suggested that the enhanced photoconductance was ascribed to electron tunneling of hot electrons generated by the surface plasmon resonance.

Preparation of diarylethene copolymers and their photoinduced refractive index change

Diarylethene copolymers were synthesized from 1-(6 0 -vinyl-2 0 -methylbenzo[b]thiophene-3 0 -yl)-2-(2 00 -methylbenzo[b]thiophene-3 00 -yl)hexafluorocyclopentene (VMBTF6) and 1-[6 0 -(4 000 -vinylbenzoyl)-2 0 -methylbenzo[b]thiophene-3 0 -yl]-2(2 00 -methylbenzo[b]thiophene-3 00 -yl)hexafluorocyclopentene (VBMBTF6) via living free radical techniques using stable TEMPO derivatives. The diarylethene content was controlled by the feed ratio of diarylethene derivatives and styrene. Transparent photochromic polymer films were prepared from the diarylethene copolymers with narrow molecular weight dispersion (PD � 1:3) by spin coating method. Photoinduced refractive index changes (DnTE) of the polymer films, with 25 mol% of diaryethene content, accompanied by the photochromic change were determined as 0.0009 and 0.0030 for poly(styrene-ran-VMBTF6) and poly(styrene-ran-VBMBTF6), respectively. 2002 Published by Elsevier Science B.V.

Effect of core atom modification on photophysical properties and singlet oxygen generation efficiencies: tetraphenylporphyrin analogues core-modified by oxygen and/or sulfur

Abstract Photophysical properties and singlet oxygen generation efficiencies of oxa- and/or thia-porphyrins have been investigated by time-resolved and steady-state spectroscopic methods. Introduction of sulfur atom into the porphyrin core induces a slight increment in the internal conversion rate and it also largely increases the intersystem crossing rate due to spin–orbit coupling enhancement, resulting the enhanced triplet state and singlet oxygen quantum yields. However, the quantum yields of mono oxygen-substituted porphyrin are reduced due to relatively more enhanced internal conversion. These suggest that sulfur modification in the core improves the photophysical efficiency of photosensitizers in the application respect of photodynamic therapy (PDT).

Nanoscale Organization of Conjugated Rods in Rod–Coil Molecules

An important challenge in the preparation of self-assembling materials is the control of supramolecular structure with well-defined shape and size, which has potential implications both fundamentally and practically in areas such as materials science, molecular electronics, and biomimetic chemistry. A typical example of a self-assembling system is provided by rod±coil molecules consisting of stiff rod and flexible coil segments. The repulsion between the covalently connected rod and coil segments leads to self-organization into a variety of supramolecular structures whose shape and size are determined by the relative volume fraction of the rod block. Recent observations from our laboratory have shown that both rod±coil diblock molecules and rod±coil multiblock copolymers containing poly(propylene oxide) as a coil segment self-assemble into layered smectic, bicontinuous cubic, and hexagonal columnar liquid-crystalline superlattices as the coil segment of the molecule increases in length relative to the rod segment. In a preliminary communication, we have demonstrated that introduction of a hydrophobic docosyl chain into the rod±coil diblock molecule based on the hydrophilic poly(ethylene oxide) coil gives rise to the formation of a discrete micellar phase with a lack of three-dimensional (3D) symmetry. In a more recent publication, rod±coil ABA triblock molecules based on poly(propylene oxide) as the coil segment were proved to self-assemble into discrete rod bundles that organize into a 3D tetragonal structure. Our approach to controlling supramolecular architecture can be extended to rod±coil systems based on a conjugated rod, which create a novel class of self-assembling materials with unique optical and electronic properties. As a result of great interest in the optically and electronically active properties of highly conjugated and stiff rod-like molecules, a variety of oligomers and polymers have been synthesized to establish the molecular structure±property relationship. Recently, however, supramolecular structure as well as chain structure has been reported to have a dramatic effect on the physical properties of conjugated molecules. Thus, manipulation of supramolecular structure in conjugated molecules is of paramount importance in achieving efficient physical properties in solid-state molecular materials. A strategy to manipulate the supramolecular structure may be accessible by incorporation of the conjugated rod into a rod±coil architecture, which would allow formation of well-defined electronically and optically active 2D sheet-like, strip-like, and hockey puck cylinder-like domains in nanoscale dimensions. It is in this context that we have synthesized coil±rod±coil triblock molecules consisting of three biphenyls connected through vinylene linkages as a conjugated rod segment and poly(propylene oxide) (PPO) as the coil segment. The synthesis of coil±rod±coil molecules with a variety of coil lengths was performed as outlined in Scheme 1. Monophenylbenzyl alcohol-terminated PPOs 1±5 were prepared from the reaction of