Sungkyunkwan University

About: Sungkyunkwan University is a education organization based out in Seoul, South Korea. It is known for research contribution in the topics: Thin film & Graphene. The organization has 28229 authors who have published 56428 publications receiving 1352733 citations. The organization is also known as: 성균관대학교.

Highly regio- and enantioselective copper-catalyzed hydroboration of styrenes

Abstract: Transition-metal-catalyzed hydroboration reactions of alkenes have attracted much interest, as they provide opportunities for unique regioand enantioselectivity. In particular, the asymmetric hydroboration of styrene derivatives to afford nonracemic a-borylated products is a useful reaction, since the resulting C B bond can be transformed with retention of configuration into a C N, C O, or C C bond. Although many catalytic systems, including ruthenium, nickel, samarium, and lanthanum catalysts, have been employed for the transformation, the development of a highly regioand enantioselective hydroboration still remains as a challenge; so far, only combinations of rhodium complexes and catecholborane (CatBH) at low temperatures have shown the desirable high regioand enantioselectivity. 5] Given the instability of catecholborane and the resulting borylated product, it is necessary to develop efficient regioselective catalytic systems that are compatible with more stable (but less reactive) hydroboration reagents, react with disubstituted olefins, and can readily be rendered enantioselective by the use of nonracemic ligands. Herein, we report that copper(I) complexes coordinated with chelating phosphine ligands can catalyze the regioand enantioselective hydroboration of styrenes with pinacolborane (PinBH) to afford the corresponding a-borated products. Reactions proceed with better than 99:1 site selectivity and with high enantioselectivity in the presence of chiral ligands for copper between room temperature and 40 8C. This process also involves the first stereoselective copper-to-boron transmetalation at a benzylic carbon atom. During our studies on the development of new enantioselective catalytic processes based on the addition of copper hydride and copper boryl reagents, we became interested in how we could make use of the Cu C bond that formed upon the addition of the copper species to electron-deficient alkenes, instead of destroying the bond by simple protonation with an alcohol. Since the in situ generation of copper hydride in the presence of pinacolborane has been suggested, we were intrigued by the possibility of forming a new hydroboration cycle with copper. Although no precedent example of metathesis between Cu C(sp) and PinBH exists, and it is known that a similar metathesis reaction between Cu C and B B is difficult, we envisioned that a copper(I) hydride coordinated with an appropriate ligand would undergo regioselective addition to styrene and facilitate an efficient transmetalation of the resulting Cu C bond with pinacolborane, rather than b-hydride elimination, to afford the desired branched boronate ester (Scheme 1).

Recent Progress in Flexible Electrochemical Capacitors: Electrode Materials, Device Configuration, and Functions

Abstract: With increasing demand for portable, flexible, and even wearable electronic devices, flexible energy storage systems have received increasing attention as a key component in this emerging field. Among the options, supercapacitors, commonly referred to as ultracapacitors or electrochemical capacitors, are widely recognized as a potential energy storage system due to their high power, fast charge/discharge rate, long cycling life-time, and low cost. To date, considerable effort has been dedicated to developing high-performance flexible supercapacitors based on various electrode materials; including carbon nanomaterials (e.g., carbon nanotubes, graphene, porous carbon materials, carbon paper, and textile), conducting polymers (e.g., polyaniline, polypyrrole, polythiophene), and hybrid materials. A brief introduction to the field is provided and the state-of-the-art is reviewed with special emphasis on electrode materials and device configurations.

Network robustness of multiplex networks with interlayer degree correlations

Abstract: We study the robustness properties of multiplex networks consisting of multiple layers of distinct types of links, focusing on the role of correlations between degrees of a node in different layers. We use generating function formalism to address various notions of the network robustness relevant to multiplex networks, such as the resilience of ordinary and mutual connectivity under random or targeted node removals, as well as the biconnectivity. We found that correlated coupling can affect the structural robustness of multiplex networks in diverse fashion. For example, for maximally correlated duplex networks, all pairs of nodes in the giant component are connected via at least two independent paths and network structure is highly resilient to random failure. In contrast, anticorrelated duplex networks are on one hand robust against targeted attack on high-degree nodes, but on the other hand they can be vulnerable to random failure.

All-solid-state spatial light modulator with independent phase and amplitude control for three-dimensional LiDAR applications

Abstract: Spatial light modulators are essential optical elements in applications that require the ability to regulate the amplitude, phase and polarization of light, such as digital holography, optical communications and biomedical imaging. With the push towards miniaturization of optical components, static metasurfaces are used as competent alternatives. These evolved to active metasurfaces in which light-wavefront manipulation can be done in a time-dependent fashion. The active metasurfaces reported so far, however, still show incomplete phase modulation (below 360°). Here we present an all-solid-state, electrically tunable and reflective metasurface array that can generate a specific phase or a continuous sweep between 0 and 360° at an estimated rate of 5.4 MHz while independently adjusting the amplitude. The metasurface features 550 individually addressable nanoresonators in a 250 × 250 μm2 area with no micromechanical elements or liquid crystals. A key feature of our design is the presence of two independent control parameters (top and bottom gate voltages) in each nanoresonator, which are used to adjust the real and imaginary parts of the reflection coefficient independently. To demonstrate this array’s use in light detection and ranging, we performed a three-dimensional depth scan of an emulated street scene that consisted of a model car and a human figure up to a distance of 4.7 m. By controlling two voltage gates separately from one another, a spatial light modulator has been made that can continuously vary the phase of 360 degrees while independently adjusting the amplitude.