Highlight Publications 2017

Dipolar Molecular Capping in Quantum Dot-Sensitized Oxides: Fermi Level Pinning Precludes Tuning Donor-Acceptor Energetics
Hai I. Wang, Hao Lu, Yuki Nagata, Mischa Bonn, and Enrique Cánovas
Dipolar Molecular Capping in Quantum Dot-Sensitized Oxides: Fermi Level Pinning Precludes Tuning Donor-Acceptor Energetics
Exploiting quantum dot (QD) nanocrystals as sensitizers of mesoporous metal oxides represents a promising path towards low cost solutions for solar energy conversion (e.g. in sensitized solar cells or in photocatalytic H2 generation). After photon absorption in the QD, an exciton is created; this exciton can be dissociated at the QD-oxide interface by a cost of energy that is given primarily by the energy difference between donor-acceptor states (QD LUMO and oxide conduction band). In this respect, reducing the energy offset between donor and acceptor is a necessary requirement for improved photoconversion efficiencies in sensitized architectures. One proposed path for reducing energy losses at QD sensitized interfaces refers to the fine tuning of donor workfunction by exploiting QD dipolar molecular capping treatments. However, previous attempts revealed a very modest gain in device efficieny induced by these treatments. In this contribution we rationalize these observations by demonstrating that Fermi level pinning at the strongly coupled QD-oxide interfaces precludes tuning donor-acceptor energetics by dipolar molecular capping. These results highlight that reducing photoconversion losses at QD sensitized interfaces by dipolar treatments will requires decoupling between the donating and accepting states (e.g. by introducing an insulating layer in bettwen QD and oxide).
© Enrique Cánovas (2017)
Can we tune interfacial electron transfer in quantum dot sensitized oxides by dipolar capping?
Single-crystal Ih ice surface: Connecting macroscopic etch pits and molecular structure
Alexandra Brumberg, Kevin D. Hammonds, Ian Baker, Ellen H. G. Backus, Patrick J. Bisson, Mischa Bonn, Charles Daghlian, Markus Mezger, Mary Jane Shultz
Single-crystal Ih ice surface: Connecting macroscopic etch pits and molecular structure
Physics and chemistry of ice surfaces are not only of fundamental interest but also have important impacts on biological and environmental processes. It is well known that the microscopic structure of the ubiquitous hexagonal ice crystal consists of stacked layers of chair-form hexagonal rings, referred to as molecular hexagons. Crystallographic unit cells can be assembled into a regular right hexagonal prism. The bases are labeled crystallographic hexagons. The molecular and crystallographic hexagons are rotated 30° relative to each other. The connection between the familiar macroscopic shape of hexagonal snowflakes and either of the hexagons is not obvious per se. Direct comparison of etch pit images, reporting on the macroscopic shape, and the electron backscatter diffraction results, providing the microscopic structure, compellingly connects the macroscopic etch pit (or: snowflake) hexagon to the crystallographic, and not molecular, hexagon.
© MPI-P (2017)
From where does the snow flake get its form? Connecting macroscopic etch pits and molecular structure of single-crystal hexagonal ice.
Photocatalytically Active Lubricant-Impregnated Surface
Sanghyuk Wooh and Hans-Jürgen Butt
Photocatalytically Active Lubricant-Impregnated Surface
We designed a new lubricant-impregnated surface which possesses photocatalytic activity as well as improved liquid repellency. This photocatalytically active lubricant-impregnated surface (PALIS) was fabricated by simple polydimethylsiloxane (PDMS) brush grafting reaction via illumination. Liquid drops slide on the PALIS by the PDMS lubricant swelled PDMS brush layer. By the combination effect of photocatalytic activity and liquid-repellency, the PALIS exhibits enhanced self-cleaning property for both dusts and organic contaminations.
© WILEY-VCH (2017)
The photocatalytically active lubricant-impregnated surface was introduced by PDMS grafting reaction on mesoporous metal-oxide photocatalysts.
Heteroatom-Doped Perihexacene from a Double Helicene Precursor: On-Surface Synthesis and Properties
Xiao-Ye Wang, Thomas Dienel, Marco Di Giovannantonio, Gabriela Borin Barin, Neerav Kharche, Okan Deniz, José I. Urgel, Roland Widmer, Samuel Stolz, Luis Henrique De Lima, Matthias Muntwiler, Matteo Tommasini, Vincent Meunier, Pascal Ruffieux, Xinliang Feng, Roman Fasel, Klaus Müllen, and Akimitsu Narita
Heteroatom-Doped Perihexacene from a Double Helicene Precursor: On-Surface Synthesis and Properties
Periacenes, which comprise two laterally peri-fused linear acenes, are an important class of zigzag-edged nanographene molecules with intriguing electronic and magnetic properties. However, the synthesis of periacenes, especially peritetracene and higher homologues, has been severely hampered by their poor stability. Herein, we report the surface-assisted synthesis of the hitherto longest periacene analogue with oxygen-boron-oxygen (OBO) segments on the zigzag edges, that is, a heteroatom-doped perihexacene. The structure was clearly visualized by scanning tunneling microscopy and noncontact atomic force microscopy. X-ray photoelectron spectroscopy and Raman spectroscopy on both the precursor and the perihexacene analogue provided further insights into the cyclodehydrogenation process. It is found that the conformation of the double helicene is highly influenced by the metal surface and the self-assembly structures. Furthermore, both the precursor and the perihexacene analogue form one-dimensional superstructures on surfaces by virtue of OBO units. The intermolecular interactions resulted from OBO segments indicate great potential for fabricating tailor-made graphene nanoarchitectures in the future.
© JACS (2017)
Heteroatom-Doped Perihexacene from a Double Helicene Precursor
Nanoparticle amount, and not size, determines chain alignment and nonlinear hardening in polymer nanocomposites
H. Samet Varol, Fanlong Meng, Babak Hosseinkhani, Christian Malm, Daniel Bonn, Mischa Bonn, Alessio Zaccone, and Sapun H. Parekh
Nanoparticle amount, and not size, determines chain alignment and nonlinear hardening in polymer nanocomposites
Polymer nanocomposites—materials in which a polymer matrix is blended with nanoparticles (or fillers)—strengthen under sufficiently large strains. Such strain hardening is critical to their function, especially for materials that bear large cyclic loads such as car tires or bearing sealants. Although the reinforcement (i.e., the increase in the linear elasticity) by the addition of filler particles is phenomenologically understood, considerably less is known about strain hardening (the nonlinear elasticity). Here, we elucidate the molecular origin of strain hardening using uniaxial tensile loading, microspectroscopy of polymer chain alignment, and theory. The strain-hardening behavior and chain alignment are found to depend on the volume fraction, but not on the size of nanofillers. This contrasts with reinforcement, which depends on both volume fraction and size of nanofillers, potentially allowing linear and nonlinear elasticity of nanocomposites to be tuned independently.
© Hasan Samet Varol (2017)
Strain hardening in polymer nanocomposites is a function of inorganic “filler” particle amount and surprisingly independent of filler size. A cancellation of filler size effects is observed because of inter-particle polymer chain alignment.
Mitochondria Targeted Protein-Ruthenium Photosensitizer for Efficient Photodynamic Applications
Sabyasachi Chakrabortty, Bikram Keshari Agrawalla, Anne Stumper, Naidu M Vegi, Stephan Fischer, Christian Reichardt, Michael Kögler, Benjamin Dietzek, Michaela Feuring-Buske, Christian Buske, Sven Rau, and Tanja Weil
Mitochondria Targeted Protein-Ruthenium Photosensitizer for Efficient Photodynamic Applications
Organelle-targeted photosensitization represents a promising approach in photodynamic therapy where the design of the active photosensitizer (PS) is very crucial. In this work, we developed a macromolecular PS with multiple copies of mitochondria-targeting groups and ruthenium complexes that displays highest phototoxicity toward several cancerous cell lines. In particular, enhanced anticancer activity was demonstrated in acute myeloid leukemia cell lines, where significant impairment of proliferation and clonogenicity occurs. Finally, attractive two-photon absorbing properties further underlined the great significance of this PS for mitochondria targeted PDT applications in deep tissue cancer therapy.
© American Chemical Society (2017)
A novel plasma protein based phototoxic, biodegradable, mitochondria targeted macromolecular photosensitizer showing significantly enhanced photodynamic behavior
 
loading content