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Li Y.,University of Waterloo | Sonar P.,Institute of Materials Research and Engineering of Singapore | Murphy L.,University of Waterloo | Hong W.,University of Waterloo
Energy and Environmental Science | Year: 2013

In recent years, the electron-accepting diketopyrrolopyrrole (DPP) moiety has been receiving considerable attention for constructing donor-acceptor (D-A) type organic semiconductors for a variety of applications, particularly for organic thin film transistors (OTFTs) and organic photovoltaics (OPVs). Through association of the DPP unit with appropriate electron donating building blocks, the resulting D-A molecules interact strongly in the solid state through intermolecular D-A and π-π interactions, leading to highly ordered structures at the molecular and microscopic levels. The closely packed molecules and crystalline domains are beneficial for intermolecular and interdomain (or intergranular) charge transport. Furthermore, the energy levels can be readily adjusted, affording p-type, n-type, or ambipolar organic semiconductors with highly efficient charge transport properties in OTFTs. In the past few years, a number of DPP-based small molecular and polymeric semiconductors have been reported to show mobility close to or greater than 1 cm2 V -1 s-1. DPP-based polymer semiconductors have achieved record high mobility values for p-type (hole mobility: 10.5 cm2 V-1 s-1), n-type (electron mobility: 3 cm2 V-1 s-1), and ambipolar (hole/electron mobilities: 1.18/1.86 cm2 V-1 s-1) OTFTs among the known polymer semiconductors. Many DPP-based organic semiconductors have favourable energy levels and band gaps along with high hole mobility, which enable them as promising donor materials for OPVs. Power conversion efficiencies (PCE) of up to 6.05% were achieved for OPVs using DPP-based polymers, demonstrating their potential usefulness for the organic solar cell technology. This article provides an overview of the recent exciting progress made in DPP-containing polymers and small molecules that have shown high charge carrier mobility, around 0.1 cm2 V-1 s-1 or greater. It focuses on the structural design, optoelectronic properties, molecular organization, morphology, as well as performances in OTFTs and OPVs of these high mobility DPP-based materials. © 2013 The Royal Society of Chemistry. Source

A comparative DFT (IEFPCM/PBE0/DGDZVP) study of the Rh-catalysed, enantioselective 1,4-addition of phenylboronic acid to 2-cyclohexenone with 11 known cyclic, chiral 1,4- and 1,5-diene ligands reveals a common pathway involving a transition state-less binding (EB) of 2-cyclohexenone to a [(diene)Rh-Ph] intermediate in a multitude of orientations leading to carborhodation (CR) via two competing, diastereomeric transition states (TS), which collapse to α-rhodioketones and then by further conformational reorganization to Rh-oxa-π-allyls. The energy difference between CR-TSs determines the enantioselectivity. DFT-predicted energy difference values are in good to excellent agreement with those derived from experimental enantiomeric excess values. Enantioselectivity was shown to be determined by a cooperative action of crossed diene coordination (measured by the angle formed by the two Rh-coordinated CC bonds in the ligand) and steric repulsion of the ligand substituents (e.g., phenyl) and 2-cyclohexenone. The cooperative effect is the strongest in the hitherto unknown 3,7-diphenylbicyclo[3.3.0]octa-2,6-diene, which was predicted to give the highest enantioselectivity of all ligands studied. This journal is © The Royal Society of Chemistry 2013. Source

Zeng H.C.,National University of Singapore | Zeng H.C.,Institute of Materials Research and Engineering of Singapore
Accounts of Chemical Research | Year: 2013

Despite significant advancements in catalysis research, the prevailing catalyst technology remains largely an art rather than a science. Rapid development in the fields of nanotechnology and materials chemistry in the past few decades, however, provides us with a new capacity to re-examine existing catalyst design and processing methods. In recent years, " nanocatalysts" has become a term often used by the materials chemistry and catalysis community. It refers to heterogeneous catalysts at nanoscale dimensions. Similar to homogeneous catalysts, freestanding (unsupported) nanocatalysts are difficult to separate after use. Because of their small sizes, they are also likely to be cytotoxic and pose a threat to the environment and therefore may not be practical for industrial use. On the other hand, if they are supported on ordinary catalyst carriers, the nanocatalysts would then revert to act as conventional heterogeneous catalysts, since chemists have known active metal clusters or oxide particles in the nanoscale regime long before the nanotechnology era. To resolve this problem, we need new research directions and synthetic strategies.Important advancements in catalysis research now allow chemists to prepare catalytic materials with greater precision. By controlling particle composition, structure, shape, and dimension, researchers can move into the next phase of catalyst development if they can bridge these old and new technologies. In this regard, one way seems to be to integrate active nanostructured catalysts with boundary-defined catalyst supports that are "not-so-nano" in dimension. However, these supports still have available hierarchical pores and cavity spaces. In principle, these devices keep the essence of traditional "catalyst-plus-support" type systems. They also have the advantages of nanoscale engineering, which involves both high level design and integration processes in their fabrication. Besides this, the active components in these devices are small and are easy to integrate into other systems. For these reasons, we refer to the final catalytic devices as integrated nanocatalysts (INCs).In this Account, we describe the current status of nanocatalyst research and introduce the various possible forms of design and types of integration for INC fabrication with increasing compositional and structural complexities. In addition, we discuss present difficulties and urgent issues of this research and propose the integration of the INCs into even more complex "supracatalysts" for future research. © 2012 American Chemical Society. Source

Kantchev E.A.B.,Institute of Materials Research and Engineering of Singapore
Chemical Communications | Year: 2011

A density functional theory study of the addition of phenylboronic acid to cyclohexenone catalyzed by chiral 1,4-diene-Rh(i) catalyst reveals that 1,4-addition is thermodynamically preferred. The enthalpy-driven enantioselection occurs during the carborhodation step and not the enone binding step, as previously proposed. The chiral ligand selectively destabilizes the disfavored transition state by making it "more early". © 2011 The Royal Society of Chemistry. Source

Li K.,Institute of Materials Research and Engineering of Singapore | Liu B.,Institute of Materials Research and Engineering of Singapore | Liu B.,National University of Singapore
Chemical Society Reviews | Year: 2014

Polymer encapsulated organic nanoparticles have recently attracted increasing attention in the biomedical field because of their unique optical properties, easy fabrication and outstanding performance as imaging and therapeutic agents. Of particular importance is the polymer encapsulated nanoparticles containing conjugated polymers (CP) or fluorogens with aggregation induced emission (AIE) characteristics as the core, which have shown significant advantages in terms of tunable brightness, superb photo- and physical stability, good biocompatibility, potential biodegradability and facile surface functionalization. In this review, we summarize the latest advances in the development of polymer encapsulated CP and AIE fluorogen nanoparticles, including preparation methods, material design and matrix selection, nanoparticle fabrication and surface functionalization for fluorescence and photoacoustic imaging. We also discuss their specific applications in cell labeling, targeted in vitro and in vivo imaging, blood vessel imaging, cell tracing, inflammation monitoring and molecular imaging. We specially focus on strategies to fine-tune the nanoparticle property (e.g. size and fluorescence quantum yield) through precise engineering of the organic cores and careful selection of polymer matrices. The review also highlights the merits and limitations of these nanoparticles as well as strategies used to overcome the limitations. The challenges and perspectives for the future development of polymer encapsulated organic nanoparticles are also discussed. © 2014 the Partner Organisations. Source

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