Jangbae Kim

A belt-shaped, blue luminescent, and semiconducting covalent organic framework.

From a synthetic viewpoint,COFs are attractive motifs since they allow total control overstructural parameters,including composition and porosity,after appropriate topological design. Most studies to datehave focused on the development of synthetic methodologieswith the aim of optimizing pore size and surface area.

Mussel‐Inspired Adhesive Binders for High‐Performance Silicon Nanoparticle Anodes in Lithium‐Ion Batteries

Conjugation of mussel-inspired catechol groups to various polymer backbones results in materials suitable as silicon anode binders. The unique wetness-resistant adhesion provided by the catechol groups allows the silicon nanoparticle electrodes to maintain their structure throughout the repeated volume expansion and shrinkage during lithiation cycling, thus facilitating substantially improved specific capacities and cycle lives of lithium-ion batteries.

A Photoconductive Covalent Organic Framework: Self‐Condensed Arene Cubes Composed of Eclipsed 2D Polypyrene Sheets for Photocurrent Generation

Covalent organic frameworks (COFs) are porous crystalline materials with predesignable 2D and 3D polymer structures. Owing to the covalent linkage of the components, as well as the elaborate control of structural parameters, including porosity and composition, COFs are promising for the design of tailor-made porous materials for gas storage. 7,8] We recently reported the cocondensation of triphenylene and pyrene monomers to create a semiconducting pconjugated COF (TP-COF). The well-defined crystalline structure of COFs should have a high probability of forming a conduction path that transports charge carriers across the framework. We are interested in the synthesis of photofunctional COFs, in particular a photoconductive COF, which would require photoinduced carrier generation and carrier transportation in the framework. Crystal engineering has demonstrated that high-quality single crystals of certain p-conjugated arenes are photoconductive as the result of exciton migration over the lattice followed by charge separation at the molecule–electrode interface. To fulfill this prerequisite, we investigated an arene-based COF, which should retain a crystal-lattice-like highly ordered arene arrangement, absorb photons in the visible region, and be robust under irradiation. Herein, we report the first example of a photoconductive COF, in which sheets composed of arene building blocks lie above one another in an eclipsed arrangement (Figure 1, PPyCOF). We chose the self-condensation of pyrenediboronic acid (Figure 1a, PDBA) as the polymerization reaction for structure formation, as we anticipated that this reaction would lead to the integration of pyrene units on edges and

Conjugated organic framework with three-dimensionally ordered stable structure and delocalized π clouds

Covalent organic frameworks are a class of crystalline organic porous materials that can utilize π–π-stacking interactions as a driving force for the crystallization of polygonal sheets to form layered frameworks and ordered pores. However, typical examples are chemically unstable and lack intrasheet π-conjugation, thereby significantly limiting their applications. Here we report a chemically stable, electronically conjugated organic framework with topologically designed wire frameworks and open nanochannels, in which the π conjugation-spans the two-dimensional sheets. Our framework permits inborn periodic ordering of conjugated chains in all three dimensions and exhibits a striking combination of properties: chemical stability, extended π-delocalization, ability to host guest molecules and hole mobility. We show that the π-conjugated organic framework is useful for high on-off ratio photoswitches and photovoltaic cells. Therefore, this strategy may constitute a step towards realizing ordered semiconducting porous materials for innovations based on two-dimensionally extended π systems.

Single nanowire on a film as an efficient SERS-active platform.

Fabricating well-defined and highly reproducible platforms for surface-enhanced Raman scattering (SERS) is very important in developing practical SERS sensors. We report a novel SERS platform composed of a single metallic nanowire (NW) on a metallic film. Optical excitation of this novel sandwich nanostructure provides a line of SERS hot spots (a SERS hot line) at the gap between the NW and the film. This single nanowire on a film (SNOF) architecture can be easily fabricated, and the position of hot spots can be conveniently located in situ by using an optical microscope during the SERS measurement. We show that high-quality SERS spectra from benzenethiol, brilliant cresyl blue, and single-stranded DNA can be obtained on a SNOF with reliable reproducibility, good time stability, and excellent sensitivity, and thus, SNOFs can potentially be employed as effective SERS sensors for label-free biomolecule detection. We also report detailed studies of polarization- and material-dependent SERS enhancement of the SNOF structure.

Role of Water in Directing Diphenylalanine Assembly into Nanotubes and Nanowires

[*] Prof. H. Ihee, J. Kim, Dr. J. Choi Center for Time-Resolved Diffraction, Department of Chemistry Graduate School of Nanoscience & Technology (WCU), KAIST 335 Gwahangno, Yuseong-gu Daejeon, 305-701 (Republic of Korea) E-mail: hyotcherl.ihee@kaist.ac.kr Prof. S. O. Kim, T. H. Han, J. S. Park Department of Materials Science and Engineering (BK21) KAIST Institute for the Nanocentury, KAIST 335 Gwahangno, Yuseong-gu Daejeon, 305-701 (Republic of Korea) E-mail: sangouk.kim@kaist.ac.kr Dr. Y. Kim Korea Research Institute of Standards and Science P.O. Box 102, Yuseong-gu Daejeon, 305-340 (Republic of Korea)

Noncovalently netted, photoconductive sheets with extremely high carrier mobility and conduction anisotropy from triphenylene-fused metal trigon conjugates.

Supramolecular assembly of small molecules via noncovalent interaction is useful for bottom-up construction of well-defined macroscopic structures. This approach is attracting increasing interest due to its high potential in manufacturing novel molecular electronic and optoelectronic devices. This Article describes the synthesis and functions of a sheet-shaped assembly from novel triphenylene-fused metal trigon conjugates. These conjugates were recently designed and synthesized by a divergent method and used for the supramolecular self-assembly of sheet-like objects. In contrast to triphenylene, which absorbs photons in ultraviolet region, the triphenylene-fused metal trigon conjugate shows a strong absorption band in the visible region. The metal trigon conjugate emits green photoluminescence with significantly enhanced quantum yield and allows intramolecular energy migration, as a result of extended pi-conjugation over metal sites. It assembles via physical gelation to form noncovalent sheets that collect a wide wavelength range of photons from ultraviolet to visible regions. The noncovalent sheets allow exciton migration and are semiconducting with an extremely large intrinsic carrier mobility of 3.3 cm(2) V(-1) s(-1). They are highly photoconductive, produce photocurrent with a quick response to light irradiation, and are capable of repetitive on-off switching. Moreover, these sheets facilitate a conduction path perpendicular to the sheet plane, thus exhibiting a spatially distinctive anisotropy in conduction. The noncovalent sheet assemblies with these unique characteristics are important for molecular optoelectronic devices based on solution-processed soft materials.

A Photoresponsive Smart Covalent Organic Framework

Ordered π-columnar structures found in covalent organic frameworks (COFs) render them attractive as smart materials. However, external-stimuli-responsive COFs have not been explored. Here we report the design and synthesis of a photoresponsive COF with anthracene units as the photoresponsive π-building blocks. The COF is switchable upon photoirradiation to yield a concavo-convex polygon skeleton through the interlayer [4π+4π] cycloaddition of anthracene units stacked in the π-columns. This cycloaddition reaction is thermally reversible; heating resets the anthracene layers and regenerates the COF. These external-stimuli-induced structural transformations are accompanied by profound changes in properties, including gas adsorption, π-electronic function, and luminescence. The results suggest that COFs are useful for designing smart porous materials with properties that are controllable by external stimuli.

Self-Assembly of Semiconducting Photoluminescent Peptide Nanowires in the Vapor Phase†

The self-assembly of bioorganic molecules, which are ubiquitous in nature, is an attractive route for fabricating functional supramolecular architectures. It also facilitates the preparation of highly ordered nanostructures by the organization of molecular building blocks through the combination of noncovalent interactions including hydrogen bonds, electrostatic interactions, p–p stacking, hydrophobic interactions, and dipole–dipole interactions. The fabrication of nanostructures through the self-assembly of peptides has attracted interest because of the unique properties of peptides, such as their functional flexibility and molecular recognition capability. In particular, the self-assembly of an aromatic dipeptide consisting of two covalently linked phenylalanine units (namely, diphenylalanine, FF), which is a key structural motif in Alzheimer s b-amyloid polypeptides, serves as an excellent model because it can spontaneously form various nanostructures in aqueous or organic environments. Herein, we report the first synthesis of semiconducting, single-crystalline, peptide-based nanowires (NWs) through a simple vapor-transport process as well as the characterization of their molecular arrangement. Single-crystalline NWs were synthesized through a simple vapor-transport process in which the linear FF peptide was used as the starting material. Powdered FF was vaporized at 250 8C in an argon atmosphere and transported downstream in a horizontal tube (see Figure S1 in the Supporting Information). Thermogravimetric analysis (TGA) shows that the peptide powder begins to vaporize at approximately 250 8C (Figure S2a). Peptide NWs were grown on a silicon substrate located downstream at 180 8C. The as-synthesized peptide NWs were well-faceted with a smooth surface and an average diameter of approximately 90 nm (Figure 1a). A gradual growth of peptide NWs occurs during the vapor-transport process (Figure S3): after the formation of nuclei on the substrate, short peptide fibrils grow into peptide NWs that are longer than 10 mm. No additional mass loss was observed by TGAup to 250 8C, which indicates a high thermal stability of the synthesized peptide NWs (Figure S2b). Figure 1b shows a selected-area electrondiffraction (SAED) pattern of a representative single peptide NW. The SAED pattern of the NW exhibits a regular spot pattern, thus indicating that the peptide NW is singlecrystalline. To investigate the crystal structure of the peptide NW a finely ground sample of the peptide NW was analyzed by powder X-ray diffraction (PXRD) at room temperature (Figure S4). Most reports previously suggested that the crystal structure of self-assembled FF nanostructures consisted of an ordered hexagonal array of normal linear dipeptide molecules. According to our results, the vapor-transport process converted linear FF into cyclo-FF, in which the terminal carboxylic acid and amine groups fused together during evaporation to form a cyclic amide bond—namely, 3,6-bis(phenylmethyl)-2,5-piperazinedione (cyclo-FF)—and with aromatic stacking between the side chains. According to the literature, dipeptides can lose water and form cyclic analogues upon heating. To unravel the molecular arrangement of NWs we performed Pawley refinement to optimize the lattice parameters and, subsequently, carried out Rietveld refinements (Figure S4) using the single-crystal structure of cyclo-FF and considering all the possible geometrical degrees of freedom. The simulated pattern fits well with the experimental PXRD pattern (Rwp= 8.82%, and RP= 6.81%, respectively) collected by using synchrotron radiation (Pohang Accelerator Laboratory, Korea); the refined lattice parameters [a= 6.18517(17) , b= 10.38349(29) , c= 23.85128(62) ] from Rietveld refinement are consistent with the SAED pattern (Figure S4). While TGA showed that the FF powder lost water at around 100 8C, the peptide NWs did not show such a water loss, which indicates that the as-synthesized peptide NWs did not contain water (Figure S2b). The NWs in this study were assembled by a vapor-transport process, with no water molecules involved. The FF molecules in the previously reported linear FF based nanotubes (NTs) assemble around central water clusters through hydrogen bonds to form a hexagonal unit cell in an aqueous environment. Vapor-phase processes often pro[*] J. S. Lee, Prof. C. B. Park Department of Materials Science and Engineering, KAIST Daejeon 305-701 (Korea) E-mail: parkcb@kaist.ac.kr

Bionanosphere Lithography via Hierarchical Peptide Self‐Assembly of Aromatic Triphenylalanine

A nanolithographic approach based on hierarchical peptide self-assembly is presented. An aromatic peptide of N-(t-Boc)-terminated triphenylalanine is designed from a structural motif for the beta-amyloid associated with Alzheimers disease. This peptide adopts a turnlike conformation with three phenyl rings oriented outward, which mediate intermolecular pi-pi stacking interactions and eventually facilitate highly crystalline bionanosphere assembly with both thermal and chemical stability. The self-assembled bionanospheres spontaneously pack into a hexagonal monolayer at the evaporating solvent edge, constituting evaporation-induced hierarchical self-assembly. Metal nanoparticle arrays or embossed Si nanoposts could be successfully created from the hexagonal bionanosphere array masks in conjunction with a conventional metal-evaporation or etching process. Our approach represents a bionanofabrication concept that biomolecular self-assembly is hierarchically directed to establish a straightforward nanolithography compatible with conventional device-fabrication processes.