Highlights 2016

Synthesis, Structure, and Chiroptical Properties of a Double [7]Heterohelicene
Xiao-Ye Wang, Xin-Chang Wang, Akimitsu Narita, Manfred Wagner, Xiao-Yu Cao, Xinliang Feng, and Klaus Müllen
Synthesis, Structure, and Chiroptical Properties of a Double [7]Heterohelicene
Double helicenes (structures with two helicenes fused together) have recently attracted great interest due to their inherent chiral properties and potential applications in asymmetric catalysis, molecular machines, and chiroptical devices. However, compared to the inspiring advances in the synthesis of higher monohelicenes, a double helicene longer than one circle of a helix has remained elusive. Herein, we report the first double [7]helicene with intramolecular π-layers, which exhibits the highest isomerization energy barrier, facilitating the separation of enantiomers by chiral HPLC and the investigation of chiroptical properties by CD spectroscopy. This work has established a new record on the way to higher double helicenes, and provided conformationally stable materials for further applications.
© ACS (2016)
Double [7]heterohelicene as a new record
High-precision estimate of the hydrodynamic radius for self-avoiding walks
Nathan Clisby and Burkhard Dünweg
High-precision estimate of the hydrodynamic radius for self-avoiding walks
The universal asymptotic amplitude ratio between the gyration radius and the hydrodynamic radius of self-avoiding walks is estimated by high-resolution Monte Carlo simulations. By studying chains of length of up to N=225≈34×106 monomers, we find that the ratio takes the value RG/RH=1.5803940(45), which is several orders of magnitude more accurate than the previous state of the art. This is facilitated by a sampling scheme which is quite general and which allows for the efficient estimation of averages of a large class of observables. The competing corrections to scaling for the hydrodynamic radius are clearly discernible. We also find improved estimates for other universal properties that measure the chain dimension. In particular, a method of analysis which eliminates the leading correction to scaling results in a highly accurate estimate for the Flory exponent of ν=0.58759700(40).
© Nathan Clisby (2016)
Typical conformation of a 5000-step self-avoiding walk on the 3D simple cubic lattice, generated by N. Clisby's highly efficient SAW-tree algorithm. The actual study used chains of up to 34 million steps.
Synthesis of graphene nanoribbons by ambient-pressure chemical vapor deposition and device integration
Zongping Chen, Wen Zhang, Carlos-Andres Palma, Alberto Lodi Rizzini, Bilu Liu, Ahmad N. Abbas, Nils Richter, Leonardo Martini, Xiao-Ye Wang, Nicola Cavani, Hao Lu, Neeraj Mishra, Camilla Coletti, Reinhard Berger, Florian Klappenberger, Mathias Kläui, Andrea Candini, Marco Affronte, Chongwu Zhou, Valentina De Renzi, Umberto del Pennino, Johannes V. Barth, Hans Joachim Räder, Akimitsu Narita, Xinliang Feng, and Klaus Müllen
Synthesis of graphene nanoribbons by ambient-pressure chemical vapor deposition and device integration
Graphene nanoribbons (GNRs), quasi-one-dimensional graphene strips, have shown great potential for nano-scale electronics, optoelectronics and photonics. Atomically precise GNRs can be “bottom-up” synthesized by surface-assisted assembly of molecular building blocks under ultrahigh vacuum conditions. However, a large-scale and efficient synthesis of such GNRs at low cost remains a significant challenge. Here we report an efficient “bottom-up” chemical vapor deposition (CVD) process for inexpensive and high-throughput growth of structurally defined GNRs with varying structures under ambient-pressure conditions. The high quality of our CVD-grown GNRs is validated by a combination of different spectroscopic and microscopic characterizations. Facile, large-area transfer of GNRs onto insulating substrates and subsequent device fabrication demonstrate their promising potential as semiconducting material, exhibiting high current on/off ratio up to 6,000 in field-effect transistor devices. This value is three orders of magnitude higher than values reported so far for other thin film transistors of structurally defined GNRs. Notably, on-surface mass-spectrometry analyses of polymer precursors provide unprecedented evidences for the chemical structures of the resulting GNRs, especially the heteroatom-doping and heterojunctions. These results pave the way toward the scalable and controllable growth of GNRs for future applications.
© ACS (2016)
High-throughput bottom-up synthesis of structurally defined graphene nanoribbons by ambient-pressure CVD process, and their unprecedentedly strong gate modulation in field-effect transistor devices.
Both Inter- and Intramolecular Coupling of O−H Groups Determine the Vibrational Response of the Water/Air Interface
Jan Schaefer, Ellen H. G. Backus, Yuki Nagata, and Mischa Bonn
Both Inter- and Intramolecular Coupling of O−H Groups Determine the Vibrational Response of the Water/Air Interface
For many geo-chemical and biological processes, interfacial water is of particular importance. However, developing an accurate understanding of its macroscopic properties requires a molecular level insight into its structure and dynamics which can be accessed by for example vibrational spectroscopy. As such, Sum Frequency Generation Spectroscopy can be used to probe the vibrational response of the first few molecular layers at interfaces. For addressing the local environment of aqueous interfacial molecules, the O−H stretch vibrational band of water is a widely employed fingerprint signal. However, it has been recognized that inter- and intramolecular coupling between O−H groups is not only critically affecting the band shape but also relevant for understanding dissipation of excess energy after chemical reactions. A unifying picture of contributing coupling effects is therefore necessary to connect the vibrational spectra with physical insight into the system. In this work, we disentangle inter- from intra-molecular coupling effects in bulk and surface water through comparison between the water O−H stretch band, for which both coupling effects are present and simple alcohols, for which intermolecular coupling dominates.
© MPI-P (2016)
Schematic picture of inter- and intramolecular coupling between O−H groups of surface water molecules probed with Vibrational Sum Frequency Generation Spectroscopy.
Spanning the Solar Spectrum: Azopolymer Solar Thermal Fuels for Simultaneous UV and Visible Light Storage
Andrew K. Saydjari, Philipp Weis, and Si Wu
Spanning the Solar Spectrum: Azopolymer Solar Thermal Fuels for Simultaneous UV and Visible Light Storage
A UV-sensitive azopolymer and a visible-light-sensitive azopolymer are combined with a fluorescent dye and a filter to create a four-layer solar thermal cell with record efficiency gravimetric energy density. While most azopolymers discharge under visible irradiation, this device can use a true solar spectrum because fluorescent down-conversion enables storage of light that would otherwise cause discharging.
© Wiley (2016)
A four-layer solar thermal cell consisting of a UV-sensitive azopolymer and a visible-light-sensitive azopolymer, combined with a fluorescent dye and a filter, is used to store solar energy.
Nonlinear control of high-frequency phonons in spider silk
Dirk Schneider, Nikolaos Gomopoulos, Cheong Y. Koh, Periklis Papadopoulos, Friedrich Kremer, Edwin L. Thomas & George Fytas
Nonlinear control of high-frequency phonons in spider silk
Spider dragline silk possesses superior mechanical properties compared with synthetic polymers with similar chemical structure due to its hierarchical structure comprised of partially crystalline oriented nanofibrils. To date, silk’s dynamic mechanical properties have been largely unexplored. Here we report an indirect hypersonic phononic bandgap and an anomalous dispersion of the acoustic-like branch from inelastic (Brillouin) light scattering experiments under varying applied elastic strains. We show the mechanical nonlinearity of the silk structure generates a unique region of negative group velocity, that together with the global (mechanical) anisotropy provides novel symmetry conditions for gap formation. The phononic bandgap and dispersion show strong nonlinear strain-dependent behaviour. Exploiting material nonlinearity along with tailored structural anisotropy could be a new design paradigm to access new types of dynamic behaviour.
© Nature Materials (2016)
Phonon band diagram for wave propagation parallel (modes 1 and 3) and normal (mode 2) to the spider silk fiber in the natural (0%) and strained (18%) state along with the theoretical prediction based on an anharmonic linear chain.
Controlling the Surface Organization of Conjugated Donor–Acceptor Polymers by their Aggregation in Solution
Mengmeng Li, Cunbin An, Tomasz Marszalek, Martin Baumgarten, He Yan, Klaus Müllen, Wojciech Pisula
Controlling the Surface Organization of Conjugated Donor–Acceptor Polymers by their Aggregation in Solution
The aggregation of conjugated polymers is found to have a significant influence on the surface organization of deposited films. Difluorobenzothiadiazole-based polymers show a strong pre-aggregation in solution, but the addition of 1,2,4-trichlorobenzene efficiently reduces such aggregates changing the surface orientation from edge- to face-on.
© Wiley (2016)
Controlling the Surface Organization of Conjugated Donor–Acceptor Polymers by their Aggregation in Solution
Near-Infrared Photoinduced Coupling Reactions Assisted by Upconversion Nanoparticles
Paul Lederhose, Zhijun Chen, Rouven Müller, James P. Blinco, Si Wu, and Christopher Barner-Kowollik
Near-Infrared Photoinduced Coupling Reactions Assisted by Upconversion Nanoparticles
We introduce nitrile imine-mediated tetrazole-ene cycloadditions (NITEC) in the presence of upconversion nanoparticles (UCNPs) as a powerful covalent coupling tool. When a pyrene aryl tetrazole derivative (λabs, max=346 nm) and UCNPs are irradiated with near-infrared light at 974 nm, rapid conversion of the tetrazole into a reactive nitrile imine occurs. In the presence of an electron-deficient double bond, quantitative conversion into a pyrazoline cycloadduct is observed under ambient conditions. The combination of NITEC and UCNP technology is used for small-molecule cycloadditions, polymer end-group modification, and the formation of block copolymers from functional macromolecular precursors, constituting the first example of a NIR-induced cycloaddition. To show the potential for in vivo applications, through-tissue experiments with a biologically relevant biotin species were carried out. Quantitative cycloadditions and retention of the biological activity of the biotin units are possible at 974 nm irradiation.
© WILEY (2016)
Schematic illustration of near-infrared photoinduced coupling reactions assisted by UCNPs.
Long-Term Repellency of Liquids by Superoleophobic Surfaces
Periklis Papadopoulos, Doris Vollmer, and Hans-Jürgen Butt
Long-Term Repellency of Liquids by Superoleophobic Surfaces
Applications of superoleophobic surfaces depend on the stability of the air cushion formed under liquid drops. To analyze the longevity of air cushions we used reflection-interference contrast microscopy (RICM) for drops on a porous fractal-like structure of sintered nanoparticles. RICM permits us to monitor the height of the air cushion with nanometer resolution. Whereas the air cushion under all investigated liquids was stable on a time scale of a few seconds to minutes and liquids rolled off, liquids with low surface tension penetrated the coating on the time scale of hours and longer. The penetration speed showed a power law dependence on time, dz/dt∼tp, the exponent p varying from −0.5 to −1.2. Thus, penetration is qualitatively different from the Lucas-Washburn law that governs spontaneous capillary filling of porous structures.
© Periklis Papadopoulos (2016)
Slow penetration of a liquid into a superoleophobic surfaces can be resolved by reflection interference contrast microscopy with nanometer resolution.
Local Time-Dependent Charging in a Perovskite Solar Cell
Victor W. Bergmann, Yunlong Guo, Hideyuki Tanaka, Ilka M. Hermes, Dan Li, Alexander Klasen, Simon A. Brotschneider, Eiichi Nakamura, Rüdiger Berger, and Stefan A. L. Weber
Local Time-Dependent Charging in a Perovskite Solar Cell
An international team of researchers from the MPI-P in Mainz and from the University of Tokyo visualized the charge distribution inside novel perovskite solar cells. They used Kelvin probe force microscopy to map the nanoscale potential distribution inside a working solar cell. They observed a slow charging process at one of the electrodes that was caused by combination of ion migration and charge trapping. This information is vital for understanding and further improving perovskite solar cells.
© ACS (2016)
Ion Migration and Charge Trapping Observed with Scanning Probe Microscopy
Microscale spatial heterogeneity of protein structural transitions in fibrin matrices
Frederik Fleissner, Mischa Bonn, Sapun H. Parekh
Microscale spatial heterogeneity of protein structural transitions in fibrin matrices
Following an injury, a blood clot must form at the wound site to stop bleeding before skin repair can occur. Blood clots must satisfy a unique set of material requirements; they need to be sufficiently strong to resist pressure from the arterial blood flow but must be highly flexible to support large strains associated with tissue movement around the wound. These combined properties are enabled by a fibrous matrix consisting of the protein fibrin. Fibrin hydrogels can support large macroscopic strains owing to the unfolding transition of α-helical fibril structures to β sheets at the molecular level, among other reasons. Imaging protein secondary structure on the submicrometer length scale, we reveal that another length scale is relevant for fibrin function. We observe that the protein polymorphism in the gel becomes spatially heterogeneous on a micrometer length scale with increasing tensile strain, directly showing load-bearing inhomogeneity and nonaffinity. Supramolecular structural features in the hydrogel observed under strain indicate that a uniform fibrin hydrogel develops a composite-like microstructure in tension, even in the absence of cellular inclusions.
© MPI-P (2016)
Protein networks – such as those in blood clots – assume different configurations (α-helices in blue and β-sheet in red) within the network based on the local force and deformation.
Synthesis of Stable Nanographenes with OBO-Doped Zigzag Edges Based on Tandem Demethylation-Electrophilic Borylation
Xiao-Ye Wang, Akimitsu Narita, Wen Zhang, Xinliang Feng, and Klaus Müllen
Synthesis of Stable Nanographenes with OBO-Doped Zigzag Edges Based on Tandem Demethylation-Electrophilic Borylation
Peritetracene, which can be regarded as a well-defined nanographene with zigzag edges, has long been pursued by chemists, but not achieved because of its high instability. In this contribution, we have developed a tandem demethylation-electrophilic borylation method to synthesize new OBO-doped peritetracenes. This work demonstrates new possibilities for the construction of zigzag-edged nanographenes, in particular higher periacenes and eventually zigzag-edged graphene nanoribbons, with excellent stability and modulated properties.
© ACS (2016)
Stable Nanographenes with OBO-Doped Zigzag Edges.
Star-Shaped Conjugated Molecules with Oxa- or Thiadiazole Bithiophene Side Arms
Kamil Kotwica, Anastasia S. Kostyuchenko, Przemyslaw Data, Tomasz Marszalek, Lukasz Skorka, Tomasz Jaroch, Sylwia Kacka, Malgorzata Zagorska, Robert Nowakowski, Andrew P. Monkman, Alexander S. Fisyuk, Wojciech Pisula, Adam Pron
Star-Shaped Conjugated Molecules with Oxa- or Thiadiazole Bithiophene Side Arms
Star-shaped conjugated molecules with oxa- or thiadiazole bithiophene side arms were investigated as promising molecules and building blocks for application in (opto)electronics and electrochromic devices.
© Wiley (2016)
Star-Shaped Conjugated Molecules with Oxa- or Thiadiazole Bithiophene Side Arms.
Fused Dibenzo[a,m]rubicene: A New Bowl-Shaped Subunit of C70 Containing Two Pentagons
Junzhi Liu, Silvio Osella, Ji Ma, Reinhard Berger, David Beljonne, Dieter Schollmeyer, Xinliang Feng, and Klaus Müllen
Fused Dibenzo[a,m]rubicene: A New Bowl-Shaped Subunit of C70 Containing Two Pentagons
Total synthetic approaches towards fullerenes are a holy grail for organic chemistry. So far, the main attempts have been focused on the synthesis of the buckminsterfullerene C60. In contrast, access to subunits of the homologue C70 remains challenging. Here, we demonstrate an efficient bottom-up synthesis of a novel bowl-shaped polycyclic aromatic hydrocarbons (PAH) with two embedded pentagons. This PAH represents a subunit of C70 and can also be seen as a nanographene molecule with defined “defects”. The bowl-shaped structure was unambiguously determined by X-ray crystallography.
© American Chemical Society (2016)
Single-crystal structure of fused Dibenzo[a,m]rubicene as a subunit of C70.
Structural Design Principle of Small Molecule Organic Semiconductors for Metal-free, Visible Light-promoted Photocatalysis
Lei Wang, Wei Huang, Run Li, Dominik Gehrig, Paul W. M. Blom, Katharina Landfester and Kai A. I. Zhang
Structural Design Principle of Small Molecule Organic Semiconductors for Metal-free, Visible Light-promoted Photocatalysis
Herein, we report on the structural design principle of small-molecule organic semiconductors as metal-free, pure organic and visible light-active photocatalysts. Two series of electron-donor and acceptor-type organic semiconductor molecules were synthesized to meet crucial requirements, such as 1) absorption range in the visible region, 2) sufficient photoredox potential, and 3) long lifetime of photogenerated excitons. The photocatalytic activity was demonstrated in the intermolecular C−H functionalization of electron-rich heteroaromates with malonate derivatives. A mechanistic study of the light-induced electron transport between the organic photocatalyst, substrate, and the sacrificial agent are described. With their tunable absorption range and defined energy-band structure, the small-molecule organic semiconductors could offer a new class of metal-free and visible light-active photocatalysts for chemical reactions.
© WILEY-VCH (2016)
Small-molecule organic semiconductor donor–acceptor systems with a tunable absorption range and defined energy-band structure are designed as metal-free, pure organic, visible-light-active photocatalysts.
Band structure engineering in organic semiconductors
Martin Schwarze, Wolfgang Tress, Beatrice Beyer, Feng Gao, Reinhard Scholz, Carl Poelking, Katrin Ortstein, Alrun A. Günther, Daniel Kasemann, Denis Andrienko, Karl Leo
Band structure engineering in organic semiconductors
A key breakthrough in modern electronics was the introduction of band structure engineering, the design of almost arbitrary electronic potential structures by alloying different semiconductors to continuously tune the band gap and band-edge energies. Implementation of this approach in organic semiconductors has been hindered by strong localization of the electronic states in these materials. We show that the influence of so far largely ignored long-range Coulomb interactions provides a workaround. Photoelectron spectroscopy confirms that the ionization energies of crystalline organic semiconductors can be continuously tuned over a wide range by blending them with their halogenated derivatives. Correspondingly, the photovoltaic gap and open-circuit voltage of organic solar cells can be continuously tuned by the blending ratio of these donors.
© Science (2016)
Molecular structural properties of (halogenated) ZnPc and SubPc.
Molecular Engineering of Conjugated Polybenzothiadiazoles for Enhanced Hydrogen Production by Photosynthesis
Can Yang, Beatriz Chiyin Ma, Linzhu Zhang, Sen Lin, Saman Ghasimi, Katharina Landfester, Kai A. I. Zhang, and Xinchen Wang
Molecular Engineering of Conjugated Polybenzothiadiazoles for Enhanced Hydrogen Production by Photosynthesis
The search for metal-free organic photocatalysts for H2 production from water using visible light remains a key challenge. Reported herein is a molecular structural design of pure organic photocatalysts, derived from conjugated polybenzothiadiazoles, for photocatalytic H2 evolution using visible light. By alternating the substitution position of the electron-withdrawing benzothiadizole unit on the phenyl unit as a comonomer, various polymers with either one- or three-dimensional structures were synthesized and the effect of the molecular structure on their catalytic activity was investigated. Photocatalytic H2 evolution efficiencies up to 116 μmol h−1 were observed by employing the linear polymer based on a phenyl-benzothiadiazole alternating main chain, with an apparent quantum yield (AQY) of 4.01 % at 420 nm using triethanolamine as the sacrificial agent.
© WILEY-VCH (2016)
Bring to light: Researchers from MPIP and Fuzhou University showed conjugated polybenzothiadiazoles as organic photocatalysts for H2 evolution from water in the presence of electron donors with visible-light irradiation.
Blocking phonon transport by structural resonances in alloy-based nanophononic metamaterials leads to ultra-low thermal conductivity
Shiyun Xiong, Kimmo Sääskilahti, Yuriy A. Kosevich, Haoxue Han, Davide Donadio, Sebastian Volz
Blocking phonon transport by structural resonances in alloy-based nanophononic metamaterials leads to ultra-low thermal conductivity
Designing the thermal conductivity of a crystalline semiconductor to approach or even be lower than the corresponding amorphous limit would aid major developments in thermoelectric energy harvesting, heat management in information and communication technology, but this remains an open challenge both conceptually and technically. Recently, researcher from MPIP, CNRS France, Aalto university Finland and Russian academic of science found a new design strategy to achieve this goal: combine the resonant and scattering mechanisms together to block the phonon transport in the whole frequency range. Through a detailed theoretical analysis, they discover that the resonances, which slow down the travel speed of thermal waves and are produced by the resonant structures outside the nanostructure, can hinder the low frequency phonon transport. While the scatterers inside the materials reduce the lifetime of phonons and are very efficient to block the high frequency phonons. With the combined mechanisms, they are able to obtain thermal conductivities in Si crystalline nanowires two times smaller than the Si amorphous value.
© Shiyun Xiong (2016)
Schematics of the scattering and resonant mechanisms: the scatter centers sit inside the material and block the original path of phonons while resonant structures locate outside the material and slow down the travel speed of phonons.
A versatile side-illumination geometry for tip-enhanced Raman spectroscopy at solid/liquid interfaces
Natalia Martín Sabanés, Leonie Driessen and Katrin F. Domke
A versatile side-illumination geometry for tip-enhanced Raman spectroscopy at solid/liquid interfaces
In-situ characterization of surfaces with tip-enhanced Raman spectroscopy (TERS) provides chemical and topographic information with high spatial resolution and sub-monolayer chemical sensitivity. To further the versatility of the TERS approach towards more complex systems such as biological membranes or energy conversion devices, adaptation of the technique to solid/liquid working conditions is essential. Here, we present a home-built side-illumination TERS setup design based on a commercial scanning tunneling microscope (STM) as a versatile, cost-efficient solution for TERS at solid/liquid interfaces. Interestingly, the results obtained from showcase resonant dye and nonresonant thiophenol monolayers adsorbed on Au single crystals suggest that excitation beam aberrations due to the presence of the aqueous phase are small enough not to limit TER signal detection. The STM parameters are found to play a crucial role for solid/liquid TERS sensitivity. Raman enhancement factors of 105 at µW laser power demonstrate the great potential the presented experimental configuration holds for solid/liquid interfacial spectroscopic studies.
© American Chemical Society (2016)
A versatile side-illumination approach for tip-enhanced Raman spectroscopy at solid/liquid interfaces provides chemical fingerprints of (sub)monolayer adsorbates with Raman enhancement factors in the order of 10^5.
Dissecting Hofmeister Effects: Direct Anion-Amide Interactions Are Weaker than Cation-Amide Binding
Vasileios Balos, Dr. Heejae Kim, Prof. Mischa Bonn, Dr. Johannes Hunger
Dissecting Hofmeister Effects: Direct Anion-Amide Interactions Are Weaker than Cation-Amide Binding
Whereas there is increasing evidence for ion-induced protein destabilization through direct ion–protein interactions, the strength of the binding of anions to proteins relative to cation–protein binding has remained elusive. In this work, the rotational mobility of a model amide in aqueous solution was used as a reporter for the interactions of different anions with the amide group. Protein-stabilizing salts such as KCl and KNO3 do not affect the rotational mobility of the amide. Conversely, protein denaturants such as KSCN and KI markedly reduce the orientational freedom of the amide group. Thus, these results provide evidence for a direct denaturation mechanism through ion–protein interactions. Comparing the present findings with results for cations shows that in contrast to common belief, anion–amide binding is weaker than cation–amide binding.
© MPI-P (2016)
Anions can hinder the rotation of amide groups in an electric field less efficient than cations as detected via the dielectric spectra of aqueous solution of N-methylacetamide.
Efficient metallic spintronic emitters of ultrabroadband terahertz radiation
T. Seifert, S. Jaiswal, U. Martens, J. Hannegan, L. Braun, P. Maldonado, F. Freimuth, A. Kronenberg, J. Henrizi, I. Radu, E. Beaurepaire, Y. Mokrousov, P. M. Oppeneer, M. Jourdan, G. Jakob, D. Turchinovich, L. M. Hayden, M.Wolf, M. Münzenberg, M. Kläui, and T. Kampfrath
Efficient metallic spintronic emitters of ultrabroadband terahertz radiation
Terahertz (THz) electromagnetic radiation is widely used for numerous applications ranging from fundamental physics and chemistry to telecommunications and forensics. So far, all solid-state emitters of THz radiation solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new, highly-efficient THz radiation source, based on the conversion of ultrafast laser-induced spin currents in metallic nanostructures into the ultrabroadband coherent THz emission fully covering the range 1 – 30 THz. Our novel source largely outperforms the traditional laser oscillator - driven solid-state THz emitters in terms of bandwidth, THz field amplitude, flexibility, scalability and cost.
© Macmillan Publishers Limited (2016)
Highly efficient gap-free THz emission is achieved via conversion of the laser-driven ultrafast spin currents into ultrafast conduction currents in a metallic ferromagnetic/non-magnetic nanostructure.
A C216-Nanographene Molecule with Defined Cavity as Extended Coronoid
Uliana Beser, Marcel Kastler, Ali Maghsoumi, Manfred Wagner, Chiara Castiglioni, Matteo Tommasini, Akimitsu Narita, Xinliang Feng, and Klaus Müllen
A C216-Nanographene Molecule with Defined Cavity as Extended Coronoid
In this work we report a solution synthesis of nanographene molecule C216 with 216 sp2 carbons, possessing a defined cavity in the center of its aromatic structure. The successful formation of the extended coronoid C216 was validated by characterizations with a combination of MALDI-TOF MS and FTIR, Raman, and UV–Vis absorption spectroscopy with theoretical supports. Remarkably, the FTIR analysis revealed finger-print peaks from C-H bonds, including the ones inside the hole, which could be explicitly reproduced by the DFT simulation. Furthermore, DFT calculations and UV-Vis spectroscopy revealed the effect of the hole on the (opto-)electronic properties of nanographene C216, showing its calculated HOMO-LUMO gap of 1.8 eV, which is 0.4 eV larger than that of the parent disk without a hole (C222).
© ACS (2016)
Structure of the novel coronoid nanographene C216
Stain-free histopathology by programmable supercontinuum pulses
Haohua Tu, Yuan Liu, Dmitry Turchinovich, Marina Marjanovic, Jens K. Lyngsø, Jesper Lægsgaard, Eric J. Chaney, Youbo Zhao, Sixian You, William L. Wilson, Bingwei Xu, Marcos Dantus, and Stephen A. Boppart
Stain-free histopathology by programmable supercontinuum pulses
The preparation, staining, visualization and interpretation of histological images of tissue are routinely used for disease diagnosis. The traditional histophathology methods have a very long history of development, and are highly time- and labor-intensive. Here, we introduce a unique optical imaging platform and methodology for label-free multimodal multiphoton microscopy, based on programmable laser supercontinuum pulses. Using this platform, the optical signatures of the tumor microenvironment, including those absent in the traditional histology, are collected directly from fresh ex-vivo mammary tissue in a matter of minutes, and without staining. The demonstrated optical platform is alignment-free and can be easily operated by medical staff not trained in optics, offering the potential to translate the stain-free molecular histopathology into routine clinical use.
© Macmillan Publishers Limited (2016)
Signatures of local tumor invasion in rat mammary specimen, revealed by high-speed optical stain-free histopathology, but absent in traditional, stained histopathology.
Mechanical Properties of Highly Porous Super Liquid-repellent Surfaces
Maxime Paven, Regina Fuchs, Taro Yakabe, Doris Vollmer, Michael Kappl, Akiko N. Itakura, and Hans-Jürgen Butt*
Mechanical Properties of Highly Porous Super Liquid-repellent Surfaces
Surfaces with self-cleaning properties are desirable for many applications. Conceptually, they are required to be highly porous on the nano- or micrometer scale, which inherently makes them mechanically weak. Optimizing the balance of mechanical strength and liquid repellency is a core aspect towards applications. However, quantitative mechanical testing of porous, super liquid-repellent surfaces is challenging due to their high surface roughness at different length scales and low stress tolerance. For this reason, mechanical testing is often performed qualitatively. Here, the mechanical responses of soot-templated super liquid-repellent surfaces are studied in detail. In particular colloidal probe force measurements cover the relevant force and length scales. By combining quantitative information from force measurements with measurements of surface wetting properties, it is shown that mechanical strength can be balanced against low wettability by tuning the reaction parameters.
© WILEY‐VCH (2016)
Mechanical properties of candle soot templated super liquid-repellent surfaces are quantitatively analyzed. The influence of the reaction parameters on the mechanical stability is revealed by colloidal probe force measurements.
Protein source and choice of anticoagulant decisively affect nanoparticle protein corona and cellular uptake
S. Schöttler, Katja Klein, K. Landfester and V. Mailänder
Protein source and choice of anticoagulant decisively affect nanoparticle protein corona and cellular uptake
There is an urgent need to understand the influence of the protein corona on nanocarriers’ interactions with cells. The decisive impact of the protein source on corona formation is regularly neglected. Major and important differences in cellular uptake of a polystyrene nanoparticle incubated in fetal bovine serum, human serum, human citrate and heparin plasma are highlighted. Protein compositions of the protein corona are determined in the respective incubation media. Interestingly, also a strong influence of heparin – a non-protein component used for anticoagulation - on cell interaction is demonstrated. While heparin enhances the uptake into macrophages, it prevents internalization into HeLa cells. Taken together we recommend that human plasma anticoagulated with citrate seems to give the most relevant results for in vitro studies of nanoparticle uptake. (adopted from © Royal Society of Chemistry)
© Royal Society of Chemistry (2016)
Incubating nanocarriers with serum and plasma yields strongly different outcomes when it comes to uptake into cells.
A Nanocapsule-Based Approach Toward Physical Thermolatent Catalysis
Ann-Christin Bijlard, Anne Hansen, Ingo Lieberwirth, Katharina Landfester, Andreas Taden
A Nanocapsule-Based Approach Toward Physical Thermolatent Catalysis
Performance under pressure is utilized as a key concept for colloidal control of reaction kinetics. Barrier nanocapsules containing a catalyst and a low-boiling-point release agent enable a highly desired, adjustable, and distinct non-Arrhenius behavior for thermoset curing. The fundamental physico-chemical approach is expected to be applicable for a broad regime of materials and catalysts. It was possible to prepare uniform and stable nanocapsules with various loads of a commercially available catalyst, thus rendering complex synthesis, labeling and registration issues (REACH, TSCA, etc.) of new catalyst molecules redundant. The release profile of the catalyst and control of the curing reaction were highly tunable by varying the catalyst loading and/or the degree of crosslinking of the polymeric shell. The threshold-temperature range was adjusted between 80 and 120 °C, which is an important regime for many technical applications. The thermolatent catalyst nanocapsules were furthermore successfully tested for the preparation of fiber-reinforced composites via resin infusion, where remarkably no filtering or clogging occurred due to the small sizes of the nanocapsules. The combination of these properties constitutes a differentiating technology and shows great promise for various important industrial applications, especially coatings, sealants, adhesives, and composites.
© John Wiley and Sons (2016)
Schematic representation of a thermolatent polymerization profile. The technology allows a highly desired combination of extended “pot life” (low viscosity required for handling) with rapid curing behavior.
Band structure of cavity-type hypersonic phononic crystals fabricated by femtosecond laser-induced two-photon polymerization
A. M. Rakhymzhanov, A. Gueddida, E. Alonso-Redondo, Z. N. Utegulov, D. Perevoznik, K. Kurselis, B. N. Chichkov, E. H. El Boudouti, B. Djafari-Rouhani and G. Fytas
Band structure of cavity-type hypersonic phononic crystals fabricated by femtosecond laser-induced two-photon polymerization
The phononic band diagram of a periodic square structure fabricated by femtosecond laser pulse-induced two photon polymerization is recorded by Brillouin light scattering (BLS) at hypersonic (GHz) frequencies and computed by finite element method. The theoretical calculations along the two main symmetry directions quantitatively capture the band diagrams of the air- and liquid-filled structure and moreover represent the BLS intensities. The theory helps identify the observed modes, reveals the origin of the observed bandgaps at the Brillouin zone boundaries, and unravels direction dependent effective medium behavior.
© Applied Physics Letters (2016)
Square patterned phononic crystal fabricated by two-photon polymerization on a zirconium propoxide based photosensitive material. Its hypersonic band structure is recorded by Brillouin scattering, and confirmed by FE calculations.
Elimination of charge carrier trapping in diluted semiconductors
D. Abbaszadeh, A. Kunz, G. A. H.Wetzelaer, J. J. Michels, N. I. Craciun, K. Koynov, I. Lieberwirth and P.W. M. Blom
Elimination of charge carrier trapping in diluted semiconductors
Electron-trapping has for decades been known to limit OLED performance. In agreement with longstanding predictions by Helfrich we show for the first time that by diluting the photoactive polymeric semiconductor with a high band-gap host, electron-trapping can be effectively eliminated. As a result, we are able to fabricate polymer light-emitting diodes with balanced electron and hole transport and reduced non-radiative trap-assisted recombination, leading to a doubling of their efficiency at nearly ten times lower material costs.
© Nature Materials (2016)
Performance of pristine (non-diluted) and diluted PLEDs: the luminous efficiency versus device current is given for different thicknesses of MEH-PPV PLEDs and 10:90 MEH-PPV: PVK and MEH-PPV: PFO blend PLEDs.
Local Flow Field and Slip Length of Superhydrophobic Surfaces
David Schäffel, Kaloian Koynov, Doris Vollmer, Hans-Jürgen Butt, and Clarissa Schönecker
Local Flow Field and Slip Length of Superhydrophobic Surfaces
While the global slippage of water past superhydrophobic surfaces has attracted wide interest, the local distribution of slip still remains unclear. Using fluorescence correlation spectroscopy, we performed detailed measurements of the local flow field and slip length for water in the Cassie state on a microstructured superhydrophobic surface. We revealed that the local slip length is finite, nonconstant, anisotropic, and sensitive to the presence of surfactants. In combination with numerical calculations of the flow, we can explain all these properties by the local hydrodynamics.
© Clarissa Schönecker (2016)
Schematic of the experimental setup: Using fluorescence correlation spectroscopy, velocities and slip length were locally resolved close to a microstructured surfaces consisting of an array of pillars
Ultrafast reorientational dynamics of leucine at the air-water interface
M. Donovan, Y. Yimer, J. Pfaendtner, E. Backus, M. Bonn, T. Weidner
Ultrafast reorientational dynamics of leucine at the air-water interface
Biology is highly dynamic. Proteins are in constant motion and their side chains are reorienting and moving on a picosecond time scale. The dynamics of side chains plays a very important role for protein binding to surfaces such as bone minerals, membranes or artificial materials. This study now establishes a methods to follow ultra fast motions at such interfaces. The dynamics of leucine amino acids is followed using a combination of time resolved sum frequency generation spectroscopy and molecular dynamics simulations.
© MPI-P (2016)
Following ultrafast motions of leucine side chains at interfaces
Vibrational Spectroscopy and Dynamics of Water
Fivos Perakis, Luigi De Marco, Andrey Shalit, Fujie Tang, Zachary R. Kann, Thomas D. Kühne, Renato Torre, Mischa Bonn, and Yuki Nagata
Vibrational Spectroscopy and Dynamics of Water
We present an overview of recent static and time-resolved vibrational spectroscopic studies of liquid water from ambient conditions to the supercooled state, as well as of crystalline and amorphous ice forms. The structure and dynamics of the complex hydrogen-bond network formed by water molecules in the bulk and interphases are discussed, as well as the dissipation mechanism of vibrational energy throughout this network. A broad range of water investigations are addressed, from conventional infrared and Raman spectroscopy to femtosecond pump–probe, photon-echo, optical Kerr effect, sum-frequency generation, and two-dimensional infrared spectroscopic studies. Additionally, we discuss novel approaches, such as two-dimensional sum-frequency generation, three-dimensional infrared, and two-dimensional Raman terahertz spectroscopy. By comparison of the complementary aspects probed by various linear and nonlinear spectroscopic techniques, a coherent picture of water dynamics and energetics emerges. Furthermore, we outline future perspectives of vibrational spectroscopy for water researches.
© ACS (2016)
Recent progress of vibrational spectroscopy including (multi-dimensional) infrared, Raman, and sum-frequency generation
Ferroelastic Fingerprints in Methylammonium Lead Iodide Perovskite
Ilka M. Hermes, Simon A. Bretschneider, Victor W. Bergmann, Dan Li, Alexander Klasen, Julian Mars, Wolfgang Tremel, Frédéric Laquai, Hans-Jürgen Butt, Markus Mezger, Rüdiger Berger, Brian J. Rodriguez, and Stefan A. L. Weber
Ferroelastic Fingerprints in Methylammonium Lead Iodide Perovskite
Methylammonium lead iodide (MAPbI 3 ) perovskite solar cells have shown a remarkable performance. However, certain phenomena and material properties, especially the possible ferroic behavior, remain unclear. Here, we report on the observation of distinct nanoscale periodic domains of MAPbI 3 (Cl) grains with piezoresponse force microscopy (PFM). The structure and the orientation of these striped domains suggest ferroelasticity as their origin. The ferroelastic twin domains could form due to the introduction of strain during the cubic−tetragonal phase transition.
© American Chemical Society (2016)
On topographically flat MAPbI 3 crystal terraces, piezoresponse force microscopy(PFM) revealed a periodic domain pattern that is characteristic for ferroelasticity.
3D Imaging of Water-Drop Condensation on Hydrophobic and Hydrophilic Lubricant-Impregnated Surfaces
Tadashi Kajiya, Frank Schellenberger, Periklis Papadopoulos, Doris Vollmer & Hans-Jürgen Butt
3D Imaging of Water-Drop Condensation on Hydrophobic and Hydrophilic Lubricant-Impregnated Surfaces
Condensation of water from the atmosphere on a solid surface is an ubiquitous phenomenon in nature and has diverse technological applications, e.g. in heat and mass transfer. We investigated the condensation kinetics of water drops on a lubricant-impregnated surface, i.e., a micropillar array impregnated with a non-volatile ionic liquid. Growing and coalescing drops were imaged in 3D using a laser scanning confocal microscope equipped with a temperature and humidity control. Different stages of condensation can be discriminated. On a lubricant-impregnated hydrophobic micropillar array these are: (1) Nucleation on the lubricant surface. (2) Regular alignment of water drops between micropillars and formation of a three-phase contact line on a bottom of the substrate. (3) Deformation and bridging by coalescence which eventually leads to a detachment of the drops from the bottom substrate. The drop-substrate contact does not result in breakdown of the slippery behaviour. Contrary, on a lubricant-impregnated hydrophilic micropillar array, the condensed water drops replace the lubricant. Consequently, the surface loses its slippery property. Our results demonstrate that a Wenzel-like to Cassie transition, required to maintain the facile removal of condensed water drops, can be induced by well-chosen surface hydrophobicity.
© Macmillan Publishers Limited (2016)
3D images and x−z cross-section of water drops condensing on an ionic liquid impregnated surface consisting of hydrophobic rectangular micropillars (w = 20 μm, s = 20 μm, h = 10 μm).
Protein adsorption is required for stealth effect of poly(ethylene glycol)- and poly(phosphoester)-coated nanocarriers
Susanne Schöttler, Greta Becker, Svenja Winzen, Tobias Steinbach, Kristin Mohr, Katharina Landfester, Volker Mailänder & Frederik R. Wurm
Protein adsorption is required for stealth effect of poly(ethylene glycol)- and poly(phosphoester)-coated nanocarriers
The current gold standard to reduce non-specific cellular uptake of drug delivery vehicles is by covalent attachment of poly(ethylene glycol) (PEG). It is thought that PEG can reduce protein adsorption and thereby confer a stealth effect. Here, we show that polystyrene nanocarriers that have been modified with PEG or poly(ethyl ethylene phosphate) (PEEP) and exposed to plasma proteins exhibit a low cellular uptake, whereas those not exposed to plasma proteins show high non-specific uptake. Mass spectrometric analysis revealed that exposed nanocarriers formed a protein corona that contains an abundance of clusterin proteins (also known as apolipoprotein J). When the polymer-modified nanocarriers were incubated with clusterin, non-specific cellular uptake was reduced. Our results show that in addition to reducing protein adsorption, PEG, and now PEEPs, can affect the composition of the protein corona that forms around nanocarriers, and the presence of distinct proteins is necessary to prevent non-specific cellular uptake.
© MPI-P (2016)
Nanocarriers (yellow) are coated with a complex multitude of proteins before they interact with cell membranes and are taken up.
Adding Four Extra K-Regions to Hexa-peri-hexabenzocoronene
Tim Dumslaff, Bo Yang, Ali Maghsoumi, Gangamallaiah Velpula, Kunal S. Mali, Chiara Castiglioni, Steven De Feyter, Matteo Tommasini, Akimitsu Narita, Xinliang Feng, and Klaus Müllen
Adding Four Extra K-Regions to Hexa-peri-hexabenzocoronene
A multistep synthesis of HBC with four additional K-regions was developed through an appropriate precursor, featuring preinstalled zigzag moieties. The stable zigzag edge-rich HBC derivative was characterized by MALDI-TOF spectrometry, Raman and IR spectroscopy, and STM. The optical properties of the modified HBC were investigated by UV/vis absorption spectroscopy, which demonstrated a significant red-shift of the absorption and lowering of the HOMO−LUMO gap compared to the parent HBC. This makes “tetrazigzag” HBC an interesting candidate for the optoelectronic applications such as in photovoltaic cells.
© ACS (2016)
Key step in the synthesis of HBC with four additional K-regions: the Scholl reaction
Nanoscale Distribution of Sulfonic Acid Groups Determines Structure and Binding of Water in Nafion Membranes
Xiao Ling, Mischa Bonn, Sapun H. Parekh, Katrin F. Domke
Nanoscale Distribution of Sulfonic Acid Groups Determines Structure and Binding of Water in Nafion Membranes
The connection between the nanoscale structure of two chemically equivalent, yet morphologically distinct Nafion fuel-cell membranes and their macroscopic chemical properties is demonstrated. Quantification of the chemical interactions between water and Nafion reveals that extruded membranes have smaller water channels with a reduced sulfonic acid head group density compared to dispersion-cast membranes. As a result, a disproportionally large amount of non-bulk water molecules exists in extruded membranes, which also exhibit larger proton conductivity and larger water mobility compared to cast membranes. The differences in the physicochemical properties of the membranes, that is, the chemical constitution of the water channels and the local water structure, and the accompanying differences in macroscopic water and proton transport suggest that the chemistry of nanoscale channels is an important, yet largely overlooked parameter that influences the functionality of fuel-cell membranes.
© Wiley (2016)
Differently cast Nafion membranes of identical chemical composition exhibit distinct nanoscale chemical constitution of the water channels. The disproportional increase of under-coordinated water molecules in membranes with smaller channel diameters correlates with improved macroscopic water and proton transport properties under the same conditions.
Modulation of Domain Size in Polycrystalline n-Type Dicyanoperylene Mono- and Bilayer Transistors
Mengmeng Li, Tomasz Marszalek, Yiran Zheng, Ingo Lieberwirth, Klaus Müllen, and Wojciech Pisula
Modulation of Domain Size in Polycrystalline n-Type Dicyanoperylene Mono- and Bilayer Transistors
Ultrathin films including mono- and bilayers of an n-type dicyanoperylene are solution-processed by dip-coating. The domain size of the polycrystalline layers is modulated via the surface roughness of the dielectric within an extremely narrow window.
© ACS (2016)
Modulation of Domain Size in Polycrystalline n-Type Dicyanoperylene Mono- and Bilayer Transistors
Light-Driven Delivery and Release of Materials Using Liquid Marbles
Maxime Paven, Hiroyuki Mayama, Takafumi Sekido, Hans-Jürgen Butt, Yoshinobu Nakamura, Syuji Fujii
Light-Driven Delivery and Release of Materials Using Liquid Marbles
Remote control of the locomotion of small objects is a challenge in itself and may also allow for the stimuli control of entire systems. Here, it is described how encapsulated liquids, referred to as liquid marbles, can be moved on a water surface with a simple near-infrared laser or sunlight. Using light rather than pH or temperature as an external stimulus allows for the control of the position, area, timing, direction and velocity of delivery. This approach makes it possible to not only transport the materials encapsulated within the liquid marble but also to release them at a specific place and time, as controlled by external stimuli. Furthermore, it is shown that liquid marbles can work as light-driven towing engines to push or pull objects. Being able to remotely transport and push/pull the small objects by light and control the release of active substances on demand should open up a wide field of conceivable applications.
© WILEY‐VCH (2016)
Scheme illustrating the light-driven delivery of material using liquid marbles (LMs).
Mengmeng Li, Cunbin An, Tomasz Marszalek, Martin Baumgarten, Klaus Müllen, Wojciech Pisula
Impact of Interfacial Microstructure on Charge Carrier Transport in Solution-Processed Conjugated Polymer Field-Effect Transistors
Surface roughness of the dielectric is precisely tuned allowing a fine control over solely the interfacial microstructure in the semicrystalline semiconductor polymer film without affecting the morphology in the upper layers. The interfacial microstructure is found to have only a minor impact on the transport originating from bypassing of interfacial defects by the charge carriers.
© Wiley (2016)
Impact of Interfacial Microstructure on Charge Carrier Transport in Solution-Processed Conjugated Polymer Field-Effect Transistors
D. W. Pilat, B. Pouligny, A. Best, T. A. Nick, R. Berger, and H.-J. Butt
Surface forces between colloidal particles at high hydrostatic pressure
It was recently suggested that the electrostatic double-layer force between colloidal particles might weaken at high hydrostatic pressure encountered, for example, in deep seas or during oil recovery. We have addressed this issue by means of a specially designed optical trapping setup that allowed us to explore the interaction of a micrometer-sized glass bead and a solid glass wall in water at hydrostatic pressures of up to 1 kbar. The setup allowed us to measure the distance between bead and wall with a subnanometer resolution. We have determined the Debye lengths in water for salt concentrations of 0.1 and 1 mM. We found that in the pressure range from 1 bar to 1 kbar the maximum variation of the Debye lengths was smaller than 1 nm for both salt concentrations. Furthermore, the magnitude of the zeta potentials of the glass surfaces in water showed no dependency on pressure.
© Rüdiger Berger, MPI-P (2016)
Surface-force measurement inside a high-pressure cell at 1000 bar: A single glass bead (yellow) was pushed against the upper wall of the glass capillary by a moderately focused trapping beam (green). The distance of the glass bead was measured by the interference of a second laser beam (red) bouncing off from the surface of the bead and from the wall.
Rethinking Superhydrophobicity
Frank Schellenberger, Noemí Encinas, Doris Vollmer, Hans-Jürgen Butt
Rethinking Superhydrophobicity
Super liquid-repellency can be achieved by nano- and microstructuring surfaces in such a way, that protrusions entrap air underneath the liquid. It is still not known, how the threephase contact line advances on such structured surfaces. In contrast to a smooth surface, where the contact line can advance continuously, on a super liquid-repellent surface the contact line has to overcome an air gap between protrusions. Here, we apply laser scanning confocal microscopy to get the first microscopic videos of water drops advancing on a superhydrophobic array of micropillars. In contrast to common belief, the liquid surface gradually bends down until it touches the top face of the next micropillars. The apparent advancing contact angle is 180°. On the receding side, pinning to the top faces of the micropillars determines the apparent receding contact angle. Based on these observations, we propose that the apparent receding contact angle should be used for characterizing super liquid-repellent surfaces, rather than the apparent advancing contact angle and hysteresis.
© American Physical Society (2016)
High-resolution imaging of a drop moving on a textured, water-repellant surface spurs researchers to propose a new definition for superhydrophobicity (a.k.a. the lotus effect).
Ambipolar Charge Transport in Isoindigo-Based Donor–Acceptor Polymers.
Romain Stalder, Sreenivasa Reddy Puniredd, Michael Ryan Hansen, Unsal Koldemir, Caroline Grand, Wojciech Zajaczkowski, Klaus Müllen, Wojciech Pisula, John R. Reynolds
Ambipolar Charge Transport in Isoindigo-Based Donor–Acceptor Polymers
A series of donor–acceptor isoindigo-based copolymers synthesized with increasing numbers of thiophene rings in the repeat unit is applied in solution-processed OFET devices. The charge transport evolved from exclusively n-type to solely p-type as the number of thiophene rings is increased to three. Solid-state NMR revealed that the choice of the donor unit length within the primary structure of the donor–acceptor polymer can be responsible for hindering its n-type character.
© ACS (2016)
Ambi- and Unipolar Charge Transport in Isoindigo-Based Donor–Acceptor Polymers
Eicosyl-substituted cyclopentadithiophene-benzothiadiazole copolymer shows a high transistor mobility und band-like transport in a microscopic scale at low temperatures.
Yu Yamashita, Felix Hinkel, Tomasz Marszalek, Wojciech Zajaczkowski, Wojciech Pisula, Martin Baumgarten, Hiroyuki Matsui, Klaus Müllen, and Jun Takeya
Mobility Exceeding 10 cm2/(Vs) in Donor–Acceptor Polymer Transistors with Band-like Charge Transport
Eicosyl-substituted cyclopentadithiophene-benzothiadiazole (C20-CDT-BTZ) copolymer exhibits even higher mobility of 11.4 cm2/Vs, than the hexadecyl-substituted derivative. The difference of mobility between C16- and C20-CDT-BTZ can be understood in terms of the microstructures investigated by grazing incidence wide angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM). a convincing transition from hopping to band-like transport is observed with increasing carrier density and temperature. In low carrier density regime, thermally-activated mobility is determined and the activation energy gradually decreases as carrier density increases. Then, above the threshold carrier density where activation energy becomes almost zero, the temperature dependence turns to be band-like. Hall effect is also found for both polymers, which indicates band-like transport in a microscopic scale as well.
© ACS (2016)
Eicosyl-substituted cyclopentadithiophene-benzothiadiazole copolymer shows a high transistor mobility und band-like transport in a microscopic scale at low temperatures.
Defect engineering: Scanning tunneling microscopy (STM) image and atomistic model of tailored heterojunctions in graphene nanoribbons (GNR)s by selective electron injection from the tip of a scanning tunneling microscope.
Klaus Müllen
Molecular defects in organic materials
In his comment Professor Klaus Müllen stimulates the discussion on molecular defects in organic materials and on the opportunity of defect engineering.
© ACS (2016)
Defect engineering: Scanning tunneling microscopy (STM) image and atomistic model of tailored heterojunctions in graphene nanoribbons (GNR)s by selective electron injection from the tip of a scanning tunneling microscope.
Photocatalytic visible light-promoted selective bromination of aromatic compounds using pure polymer-based catalyst at room temperature.
Run Li, Zi Jun Wang, Lei Wang, Beatriz Chiyin Ma, Saman Ghasimi, Hao Lu, Katharina Landfester, and Kai. A. I. Zhang
Photocatalytic Selective Bromination of Electron-Rich Aromatic Compounds Using Microporous Organic Polymers with Visible Light
No more harsh reaction conditions needed! Pure organic, heterogeneous, metal-free, and visible light-active photocatalysts offer a more sustainable and environmentally friendly alternative to traditional metal-based catalysts. Here we report a series of microporous organic polymers containing photoactive conjugated organic semiconductor units as heterogeneous photocatalysts for a visible-light-promoted, highly selective bromination reaction of electron-rich aromatic compounds using HBr as a bromine source and molecular oxygen as a clean oxidant.
© ACS (2016)
Photocatalytic visible light-promoted selective bromination of aromatic compounds using pure polymer-based catalyst at room temperature.
Schematic representation of reactions and polymerizations at the interface of two immiscible liquids.
Keti Piradashvili, Evandro M. Alexandrino, Frederik R. Wurm, and Katharina Landfester
Reactions and Polymerizations at the Liquid–Liquid Interface
The confinement of two reactants at the interface to form a new product can be advantageous in terms of improved reaction kinetics, higher yields, and selectivity. A general overview on low molecular weight organic chemistry is given, and the applications of heterophase polymerization, occurring at or in proximity of the interface, (mostly) in emulsions are presented. This strategy can be used for the efficient production of nano- and microcarriers for various applications.
© MPI-P (2016)
Schematic representation of reactions and polymerizations at the interface of two immiscible liquids.
 
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