Using upconversion nanoparticles to probe brain function

Prof LIU Xiaogang, together with an international research team, developed a novel approach to investigate deep brain stimulation utilising upconversion nanoparticles. These unique nanoparticles, which is pioneered by Prof LIU's research group, allow visible light to be delivered deep into the brain in control of neural activities in a less-invasive manner, marking a significant breakthrough which could empower researchers to uncover valuable insights about the brain. This exciting piece of work was published in Science on 9 Feb 18. Read More.


Solar Driven Conversion of Carbon Dioxide to Ethylene

Asst Prof YEO Boon Siang Jason and his co-workers have developed an artificial photosynthesis device that facilitates the conversion of carbon dioxide into ethylene with state-of-the-art efficiencies.


Highly efficient on-chip direct electronic-plasmonic transducers

Assoc Prof Christian NIJHUIS and his research group from the Department of Chemistry, NUS have developed electronic-plasmonic transducers operating at optical frequencies with high efficiencies which are important to bridge high speed photonics and nanoscale electronics. For integrated circuit (IC) technology, there is a need for optical elements and high speed interconnects with small footprints. Surface plasmon polaritons, which can be seen as light-confined to sub-wavelength dimensions, can carry information at high speeds but they are not diffraction limited. By coupling two electronic-plasmonic transducers based on metal-insulator-metal (MIM) tunnel junctions via a plasmonic waveguide, the researchers have demonstrated on-chip generation, manipulation and detection of these surface plasmons. This work has recently been published in Nature Photonics, 11, 623–627 (2017) doi: 10.1038/s41566-017-0003-5


Photoredox Functionalizaton of C(sp3)-H Bonds

Asst Prof WU Jie and his research group from the Department of Chemistry, NUS have developed a visible-light-promoted Ni-catalyzed C(sp3)-H alkenylation of ethers and amides with excellent selectivity in a green fashion. The functionalization of carbon–hydrogen (C–H) bonds is one of the most attractive strategies for molecular construction in organic synthesis, owing to its relative abundance in organic molecules and its availability for functionalization at almost any stage in a synthetic sequence. Through the synergistic combination of photoredox and Ni catalysis, the direct C(sp3)-H alkenylation was achieved in an atom-efficient, additive-free, and ligand-free manner. An unusual regioselectivity was observed for the alkenylation, which was complementary to that of conventional radical addition processes. Mechanistic investigation indicatesd a rare example of nickel-hydride generation with C(sp3)-H bonds as the hydride source. This work has recently been published in J. Am. Chem. Soc. (DOI: 10.1021/jacs.7b08158).


Molecular electronics scientists shatter 'impossible' record of rectification rate

Assoc Prof Christian NIJHUIS from the Department of Chemistry, NUS and his research team, in collaboration with Dr Damien Thompson (University of Limerick) and Prof Enrique del Barco (University of Central Florida), have fabricated molecular diodes with a rectification ratio (the ratio between the forward and reverse current) of nearly one million. The rectification ratio is a measure of the switching performance of the device. Although the value is similar to that of conventional diodes, it is achieved at much smaller physical dimensions. These diodes change the number of molecules contributing to charge transport only in forward bias but not in the opposite direction due to electrostatic switching. This breakthrough represents another step towards realising nano-electronic devices based on molecular systems. (NATURE NANOTECHNOLOGY, DOI: 10.1038/nnano.2017.110)


Gate-Tunable Giant Stark Effect in Few-Layer Black Phosphorus

Two-dimensional black phosphorus has sparked enormous research interest due to its high carrier mobility, layer-dependent direct bandgap and outstanding in-plane anisotropic property. It is one of the few 2D materials where it is possible to tune the bandgap over a wide energy range from the visible to the IR spectrum. A team led by Assistant professor Lu Jiong has demonstrated an electrical field-controlled giant Stark effect in black phosphorus for potential applications in advanced electro-optic devices. This work has recently been published in Nano Letters (DOI:10.1021/acs.nanolett.6b05381) and highlighted in Nature Photonics (doi:10.1038/nphoton.2017.102).


Reversible multi-electron redox chemistry of π-conjugated N-containing heteroaromatic molecule-based organic cathodes

Even though organic molecules with well-designed functional groups can be programmed to have high electron density per unit mass, their poor electrical conductivity and low cycle stability limit their applications in batteries. A team led by Prof Loh Kian Ping report the facile synthesis of π-conjugated quinoxaline-based heteroaromatic molecules (3Q) by condensation of cyclic carbonyl molecules with o-phenylenediamine. 3Q features a number of electron-deficient pyrazine sites, where multiple redox reactions take place, which was probed using in-situ 15N and 13C solid state Nuclear Magnetic Resonance. When hybridized with graphene and coupled with an ether-based electrolyte, an organic cathode based on 3Q molecules displays a discharge capacity of 395 mAh g−1 at 400 mA g−1 (1C) in the voltage range of 1.2–3.9 V and a nearly 70% capacity retention after 10,000 cycles at 8 A g−1. This work is important in demonstrating that heteroaromatic molecules with multiple redox sites are promising in developing high-energy-density, long-cycle-life organic rechargeable batteries.


Cobalt-Catalyzed Asymmetric Hydroboration/Cyclization of 1,6-Enynes and Enantioselective Synthesis of (-)-Magnofargesin

Dr. Ge and his research team in the Department of Chemistry, NUS, have developed the first cobalt-catalyzed enantioselective hydroboration/cyclization of 1,6-enynes to prepare chiral five-membered cyclic organic compounds. In addition, they applied this methodology to synthesize a bioactive natural product (-)-magnofargesin. This work has recently been published in J. Am. Chem. Soc. (DOI: 10.1021/jacs.7b01708).


NUS chemists made C-C coupling based 2D polymer

Professor Kian Ping Loh and PhD student Liu Wei in the Department of Chemistry, National University of Singapore, applied an ingenious strategy based on endogenous polymerization, carried out without catalyst, solvent or initiator, to make 2-D polymer based on C-C coupling reactions.
They discovered that pre-ordering well-designed, flat monomers into a single crystal structure can lead to a 2D crystalline aromatic polymer upon thermal annealing. The achieved polymeric sheets are parallel and can be readily exfoliated into micrometer-sized sheets with nanometer thickness, similar to the case of single-layer graphene. This approach paves the way towards the controlled synthesis of extended crystalline 2D conjugated materials for various applications. Due to its intra-sheet conjugation and ordered open 1D channel, the 2D polymer fabricated by Loh et. al. exhibits unprecedented cycle stability and rate capability when applied as an anode in an ambient temperature sodium cell. The work is published in Nature Chemistry. Link


Toward metallic molecular wires!

Graphene nanoribbons (GNRs) with a width < 10 nm have promising applications in the future nano-electronics. While semi-conducting GNRs can be applied as active components in field effect transistors, the metallic GNRs can be used as conducting wires. So far, the synthesis of GNRs with potential metallic properties is still not successful. In a recent publication in Link, A/P Wu Jishan’s group reported the challenging synthesis and physical characterizations of a series of soluble and stable rylene ribbon molecules with the record length, which can serve as good model compounds of the narrowest armchair graphene nanoribbon. They observed very unusual open-shell diradical character for long rylene molecules, which can be correlated to the potential metallic property of the infinite polyrylene ribbon. This work was selected as a cover in the January issue.


Extended Bis(benzothia)-quinodimethanes and Their Dications: From Singlet Diradicaloids to Isoelectronic Structures of Long Acenes

In a recent article published in Angew. Chem. Int. Ed., 2016, 55, 9316-9320 (hot paper), (Link), Dr. Chi and her co-workers synthesized a series of extended bis(benzothia)-quinodimethanes and their dications as stable species. The neutral compounds mainly have a quinoidal structure in the ground state but show increased diradical character with extension of the central quinodimethane unit. More importantly, the dications exhibit similar electronic absorption spectra, NMR spectra, NICS values, and diatropic ring currents to their aromatic all-carbon acene analogues and thus can be regarded as genuine isoelectronic structures of pentacene, hexacene and heptacene, respectively. This study provides a new way to design and synthesize stable longer acene analogues with similar electronic structures to the traditional all-carbon acenes.


Boronic Acid: A Bio-Inspired Strategy to Increase the Sensitivity and Selectivity of Fluorescent NADH Probe

Fluorescent probes have been widely used in the molecular recognition events in biological systems; however, it remains challenging to design small-molecule fluorescent probes sensitively and selectively sensing biomolecules with complex structures. Inspired by the enzyme-catalyzed reaction between biomolecule and probe, Prof. Chang and collaborators present a novel combination-reaction two-step sensing strategy to improve sensitivity and selectivity. Based on this strategy, they successfully prepared a boronic acid based fluorescent NADH (reduced nicotinamide adenine dinucleotide) probe and evaluate NADH levels in live cell imaging.
J. Am. Chem. Soc., 2016138 (33), pp 10394–10397
Link


Taming image press

Development of background-free tame fluorescent probes for intracellular live cell imaging

Fluorescent dyes have been used for bioimaging for long time, but the conventional wisdom says the organic dyes are sticky and leave high background in the biological system. Prof. Chang and collaborators dreamed no-background imaging probes and challenged to figure the physico-chemical properties of such ideal dyes. By testing fluorescent library combined with chemoinformatic analysis, they found three main parameters to achieve the holy grail. The process they called “taming” and the tamed dyes will be of general use for future bioimaging. 


Dr Chi - Figure for paper-1

Dipolar Quinoidal Acene Analogues as Stable Isoelectronic Structures of Pentacene and Nonacene

In a recent article published in Angew. Chem. Int. Ed., 2015, 54, 14412 (Link ), Dr. Chi and her co-workers synthesized quinoidal thia- acene analogues as the respective isoelectronic structures of pentacene and nonacene and an unusual 1,2-sulfur migration was observed during the Friedel-Crafts alkylation reaction. They display a closed-shell quinoidal structure in the ground state with a distinctive dipolar character. In contrast to their acene isoelectronic structures, both compounds are very stable because of existence of more aromatic sextet rings, dipolar character, and kinetic blocking. They exhibit unique packing in single crystals due to balanced dipole-dipole and [C-H•••π]/[C-H•••S] interactions.


Dr Chi - Figure for paper-2

Z-Shaped Pentaleno- Acene Dimers with High Stability and Low Band Gap

Dr. Chi’s group reported a new strategy to stabilize reactive acenes by fusion of an anti-aromatic pentalene unit onto the zig-zag edges of two acene units to form a Z-shaped acene dimer, which turned out to be extremely stable and show a small energy gap due to intramolecular donor-acceptor interaction. The stability of pentaleno- tetracene dimer solution is up to 54 days in ambient air and light conditions. X-ray crystallographic analysis revealed their unique geometry and 1D slip-stack columnar structure.
Reference: Angew. Chem. Int. Ed. 2016 (Link


Dielectric Medium

Self-consistent reaction field (SCRF) methods based on multiple expansions

Self-consistent reaction field (SCRF) methods based on multiple expansions are the most popular approaches in incorporation solvation effect in quantum chemical calculations. The Onsager SCRF model was first implemented in the most popular and widely used Gaussian series of programs by Wong, Frisch and Wiberg. The implementation and application of this SCRF method were described in Journal of American Chemistry Society (1991, 113, 4776-4782). The total citations of this landmark paper have reached 1000 recently!


Multiphoton harvesting metal

Multiphoton harvesting metal–organic frameworks

Usually multiphoton harvesting property exhibited by the organic molecules in the solution, is quenched in the solid state due to aggregation. However, efficiently luminescent materials in the solid-state form are highly preferable in many photonic applications such as upconversion lasing and light emission due to a higher resistant to photobleaching. By rational choice of ligands with high second hyperpolarizability, MOFs with large nonlinear optical response (up to direct absorption of four photons at 1500 nm) has been reported for the first time by Hong Sheng Quah, Weiqiang Chen, Martin K. Schreyer, Hui Yang, Ming Wah Wong, Wei Ji, and Jagadese J. Vittal in the recent issue of Nature Communications (Vol. 6, Article No. 7954, 2015, doi:10.1038/ncomms8954).
Link


LXG_Nature Nanotechnology

Nature Nanotechnology

Assoc Professor LIU Xiaogang group reported that producing luminescence materials with tunable emission colors that can be applied for high quality displays is a very difficult task. Especially, it is challenging to develop light-responsive materials that are possible to produce any desired colors in a broad spectrum range on demand through the use of a simple external stimulus. Now they have achieved this goal by exploiting a novel concept, non-steady-state upconversion, based on the design and synthesis of lanthanide-doped core-shell upconversion nanomaterials. The emission color of the core-shell upconversion nanocrystals was turned by adjusting the pulse width and intensity of near-infrared laser excitations. R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, X. Liu, “Temporal full-color tuning through non-steady-state upconversion, ” Nature Nanotechnology, 2015, 10, 237-242. Link


Milk orange

Illuminating test measures fat in milk

Prof. Chang Young-Tae’s group reported the first fluorescent milk fat sensor (Chem Comm, 2014, 50, 10398-10410). It exhibits magnificent, yet selective turn-on feature towards fat molecules in complicated milk matrix, through the disaggregation-induced emission mechanism. Further construction of a handy fluorescence milk fat detector provides a convenient rapid tool to measure fat amount quantitatively. This discovery may greatly help enhance the milk quality control process.This work was highlighted in Chemistry World: Link


Reuleaux Triangle Disks

Reuleaux Triangle Disks: New Shape on the Block (DOI: ja506625y)

A/P Fan Wai Yip and Bernard Ng Choon Hwee reported the preparation of Reuleaux triangle disks from the hydrolysis and precipitation of bismuth nitrate in an ethanol-water system with 2,3-bis(2-pyridyl)pyrazine. Analysis of the intermediates provided insights into the formation of the Reuleaux triangle disk, revealing a unique growth process.


Mulitcolor_barcoding

Multicolor Barcoding in a Single Upconversion Crystal

The synthesis of luminescent crystals based on hexagonal-phase sodium yettrium fluoride upconversion microrods is reported by A/P Liu Xiaogang's group. The synthetic procedure involves an epitaxial end-on growth of upconversion nanocrystals comprising different lanthanide activators onto the NaYF4 microrods. This bottom-up method readily affords multicolor-banded crystals in gram quantity by varying the composition of the activators. Importantly, the end-on growth method using one-dimensional microrods as the template enables facile multicolor tuning in a single crystal, which is inaccessible in conventional upconversion nanoparticles. These novel materials offer opportunities as optical barcodes for anti-counterfeiting and multiplexed labeling applications.


JJ Vittal - Single Crystals

Single crystals of a coordination polymer containing an organic polymer ligand!

Prof. JJ Vittal’s group reported an organic polymer comprising cyclobutane rings and a coordination polymer blend together inside this 3D structure obtained in a photochemical dimerization reaction (Angewandte Chemie, 2014). The organic polymer can be depolymerized by the cleavage of cyclobutane rings in an SCSC manner. Read More


JJ Vittal - Reversible Single Crystals

You can be made and broken in cycles, Mr. C-C Bond!

The cyclobutane ring can easily be made by solid-state [2+2] cycloaddition reaction. But can this be cleaved? Is it possible to make and break the C-C bond reversible? Can this be achieved in a single-crystal to single-crystal manner? Will this be accompanied by change in properties like photoluminescence? If so the applications for these types of systems are eminent in molecular switching and data storage. For more information see Prof. JJ Vittal’s recent Angewandte Chemie, 2014. Read More


JJ Vittal - Single Crystals Popping

Crystals dance during a reaction! Of course they are excited under UV light!

The self-propulsion of single crystals of three Zn(II) complexes under UV light has been discovered by Prof. JJ Vittal’s group (Angewandte Chemie, 2014). This visually appealing demonstration of the utility of molecular materials for conversion of energy to work. This has been considered as a hot paper by the journal and highlighted as their cover story of the issue. Read More


JJ Vittal - Distortional Supramolecular

Distortional isomerism in polyrotaxane coordination polymers!

Of the four supramolecular isomers of coordination polymers synthesized, two have polyrotaxane structures which differ only in the relative positions of the wheel in the neighboring axle. They show different photoreactivity under UV light as well as sensing abilities of a number of organic nitro compounds. Prof. JJ Vittal’s group reported these findings in Angewandte Chemie, 2014. Read More


Wu JS - Graphics 20131226

N

A new benchmark dye for dye-sensitized solar cell! In a recent Article published in JACS (Link), A/P Wu Jishan and his local/international collaborators synthesized a series of N-annulated perylene substituted and fused porphyrin dyes, which showed largely enhanced light harvesting capability in particular in the near infrared region. As a result, one of the dyes exhibited a power conversion efficiency of around 11%, which is comparable and even slightly higher than that of the benchmark dye YD2-o-C8 under same conditions.


Loh KP - TOC

Observing High Pressure Chemistry in Graphene Bubbles

The above recent work by the team of Professor Loh Kian Ping has been chosen as a "Hot Paper" by the editors of Angewandte Chemie for its importance in a rapidly evolving field of high current interest. It is also highlighted in Chemistry World published by Royal Society of Chemistry.
Reference: C H Y X Lim, M Nesladek and K P Loh, Angew. Chem., Int. Ed., 2013, DOI: 10.1002/ange.201308682


Wu JS - Graphics 20131121

Dibenzoheptazethrene Isomers with Different Biradical Characters: An Exercise of Clar’s Aromatic Sextet Rule in Singlet Biradicaloids

Extension of the Clar’s Aromatic Sextet Rule to the singlet biradicaloids!
In a recent Article published in JACS (Link), A/P Wu Jishan and his local/international collaborators demonstrated that Clar’s Aromatic Sextet Rule can be further extended from the closed-shell polycyclic aromatic hydrocarbons to the open-shell polycyclic hydrocarbon systems, and provides an important guideline for the design of singlet biradicaloids with tailored biradical character and tunable optical, electronic and magnetic properties.


Loh KP Abstract - ncomms3681

Order–disorder Transition in a Two-dimensional Boron–Carbon–Nitride Alloy

A team lead by Professor Loh Kian Ping reported the mixing and demixing of 2-D boron–nitrogen and carbon phases and found that energetics for such processes are modified by the metal substrate. The brick-and-mortar patchwork observed of stoichiometrically percolated hexagonal boron–carbon–nitride domains surrounded by a network of segregated graphene nanoribbons can be described within the Blume–Emery–Griffiths model applied to a honeycomb lattice.The isostructural boron nitride and graphene assumes remarkable fluidity and can be exchanged entirely into one another by a catalytically assistant substitution. Visualizing the dynamics of phase separation at the atomic level provides the premise for enabling structural control in a 2-D network for broad nanotechnology applications
Read more: Link