Publications by authors named "Stefan Hecht"

183 Publications

Accelerated Discovery of α-Cyanodiarylethene Photoswitches.

J Am Chem Soc 2021 Jun 11. Epub 2021 Jun 11.

DWI-Leibniz Institute for Interactive Materials & Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, Forckenbeckstrasse 50, Aachen 52074, Germany.

Cyanodiarylethene chromophores are able to undergo constitutional exchange via dynamic covalent chemistry (DCC). During this process, the central ethylene bridge of the molecular scaffold can be broken and thereby enables the assembly of a new combination of aryl moieties around the reformed ethylene bridge. The reversible C═C double bond exchange has exemplarily been investigated using α-cyanostilbenes. Establishing a dynamic equilibrium reaction from α-cyanodiarylethene with arylacetonitriles under mild conditions has been the basis to access constitutional libraries of new photoswitches with potentially improved properties. When subject to irradiation with light of adequate wavelength, α-cyanodiarylethenes undergo / isomerization followed by ring-closure. By screening the thus accessible dynamic chromophore libraries using a desired detection wavelength, we could identify specific dithienyl analogues that exhibit three-state photochromism. The combination of dynamic constitutional libraries of functional chromophores in combination with the light-guided screening and selection should lead to more rapid exploration of structural diversity dye chemistry.
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http://dx.doi.org/10.1021/jacs.1c03631DOI Listing
June 2021

Tough Multimaterial Interfaces through Wavelength-Selective 3D Printing.

ACS Appl Mater Interfaces 2021 May 30;13(18):22065-22072. Epub 2021 Apr 30.

Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, United States.

Strong and well-engineered interfaces between dissimilar materials are a hallmark of natural systems but have proven difficult to emulate in synthetic materials, where interfaces often act as points of failure. In this work, curing reactions that are triggered by exposure to different wavelengths of visible light are used to produce multimaterial objects with tough, well-defined interfaces between chemically distinct domains. Longer-wavelength (green) light selectively initiates acrylate-based radical polymerization, while shorter-wavelength (blue) light results in the simultaneous formation of epoxy and acrylate networks through orthogonal cationic and radical processes. The improved mechanical strength of these interfaces is hypothesized to arise from a continuous acrylate network that bridges domains. Using printed test structures, interfaces were characterized through spatial resolution of their chemical composition, localized mechanical properties, and bulk fracture strength. This wavelength-selective photocuring of interpenetrating polymer networks is a promising strategy for increasing the mechanical performance of 3D-printed objects and expanding light-based additive manufacturing technologies.
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http://dx.doi.org/10.1021/acsami.1c06062DOI Listing
May 2021

Chirality Remote Control in Nanoporous Materials by Circularly Polarized Light.

J Am Chem Soc 2021 May 29;143(18):7059-7068. Epub 2021 Apr 29.

Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.

The ability to dynamically control chirality remains a grand challenge in chemistry. Although many molecules possess chiral isomers, lacking their isolation, for instance during photoisomerization, results in racemic mixtures with suppressed enantiospecific chiral properties. Here, we present a nanoporous solid in which chirality and enantioselective enrichment is induced by circularly polarized light (CPL). The material is based on photoswitchable fluorinated azobenzenes attached to the scaffold of a crystalline metal-organic framework (MOF). The azobenzene undergoes -to--photoisomerization upon irradiation with green light and reverts back to upon violet light. While each moiety in conformation is chiral, we show the isomer also possesses a nonplanar, chiral conformation. During photoisomerization with unpolarized light, no enantiomeric enrichment is observed and both isomers, - and - as well as and -, respectively, are formed in identical quantities. In contrast, CPL causes chiral photoresolution, resulting in an optically active material. Right-CPL selectively excites - and - enantiomers, producing a MOF with enriched -enantiomers, and . The induction of optical activity is reversible and only depends on the light-handedness. As shown by first-principle DFT calculations, while both, and , are stabilized in nonplanar, chiral conformations in the MOF, the isomer adopts a planar, achiral form in solution, as verified experimentally. This shows that the chiral photoresolution is enabled by the linker reticulation in the MOF. Our study demonstrates the induction of chirality and optical activity in solid materials by CPL and opens new opportunities for chiral resolution and information storage with CPL.
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http://dx.doi.org/10.1021/jacs.1c01693DOI Listing
May 2021

Photocontrollable Modulation of Frontier Molecular Orbital Energy Levels of Cyclopentenone-Based Diarylethenes.

J Phys Chem A 2021 May 22;125(17):3681-3688. Epub 2021 Apr 22.

N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47, Leninsky prosp, 119991 Moscow, Russian Federation.

Photoswitchable diarylethenes provide a unique opportunity to optically modulate frontier molecular orbital energy levels, thereby opening an avenue for the design of electronic devices such as photocontrollable organic field-effect transistors (OFETs). In the present work, the absolute position of the frontier orbital levels of nonsymmetrical diarylethenes based on a cyclopentenone bridge has been studied using cyclic voltammetry and density functional theory (DFT) calculations. It has been shown that varying heteroaromatic substituents make it possible to change the absolute positions of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of both diarylethene photoisomers. The data obtained are used to refine the operation mechanism of the previously developed OFET devices, employing the cyclopentenone-derived diarylethenes at the dielectric/semiconductor interface.
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http://dx.doi.org/10.1021/acs.jpca.1c01836DOI Listing
May 2021

Multiresponsive Nonvolatile Memories Based on Optically Switchable Ferroelectric Organic Field-Effect Transistors.

Adv Mater 2021 Apr 3;33(14):e2007965. Epub 2021 Mar 3.

Université de Strasbourg, CNRS, ISIS UMR 7006, 8 alleé Gaspard Monge, Strasbourg, 67000, France.

Organic transistors are key elements for flexible, wearable, and biocompatible logic applications. Multiresponsivity is highly sought-after in organic electronics to enable sophisticated operations and functions. Such a challenge can be pursued by integrating more components in a single device, each one responding to a specific external stimulus. Here, the first multiresponsive organic device based on a photochromic-ferroelectric organic field-effect transistor, which is capable of operating as nonvolatile memory with 11 bit memory storage capacity in a single device, is reported. The memory elements can be written and erased independently by means of light or an electric field, with accurate control over the readout signal, excellent repeatability, fast response, and high retention time. Such a proof of concept paves the way toward enhanced functional complexity in optoelectronics via the interfacing of multiple components in a single device, in a fully integrated low-cost technology compatible with flexible substrates.
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http://dx.doi.org/10.1002/adma.202007965DOI Listing
April 2021

Proton-Gated Ring-Closure of a Negative Photochromic Azulene-Based Diarylethene.

Angew Chem Int Ed Engl 2020 Oct 19;59(42):18532-18536. Epub 2020 Aug 19.

Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany.

Proton-responsive photochromic molecules are attractive for their ability to react on non-invasive rapid optical stimuli and the importance of protonation/deprotonation processes in various fields. Conventionally, their acidic/basic sites are on hetero-atoms, which are orthogonal to the photo-active π-center. Here, we incorporate azulene, an acid-sensitive pure hydrocarbon, into the skeleton of a diarylethene-type photoswitch. The latter exhibits a novel proton-gated negative photochromic ring-closure and its optical response upon protonation in both open and closed forms is much more pronounced than those of diarylethene photoswitches with hetero-atom based acidic/basic moieties. The unique behavior of the new photoswitch can be attributed to direct protonation on its π-system, supported by H NMR and theoretical calculations. Our results demonstrate the great potential of integrating non-alternant hydrocarbons into photochromic systems for the development of multi-responsive molecular switches.
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http://dx.doi.org/10.1002/anie.202007989DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7589205PMC
October 2020

Xolography for linear volumetric 3D printing.

Nature 2020 12 23;588(7839):620-624. Epub 2020 Dec 23.

Department of Chemistry and IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin, Germany.

The range of applications for additive manufacturing is expanding quickly, including mass production of athletic footwear parts, dental ceramics and aerospace components as well as fabrication of microfluidics, medical devices, and artificial organs. The light-induced additive manufacturing techniques used are particularly successful owing to their high spatial and temporal control, but such techniques still share the common motifs of pointwise or layered generation, as do stereolithography, laser powder bed fusion, and continuous liquid interface production and its successors. Volumetric 3D printing is the next step onward from sequential additive manufacturing methods. Here we introduce xolography, a dual colour technique using photoswitchable photoinitiators to induce local polymerization inside a confined monomer volume upon linear excitation by intersecting light beams of different wavelengths. We demonstrate this concept with a volumetric printer designed to generate three-dimensional objects with complex structural features as well as mechanical and optical functions. Compared to state-of-the-art volumetric printing methods, our technique has a resolution about ten times higher than computed axial lithography without feedback optimization, and a volume generation rate four to five orders of magnitude higher than two-photon photopolymerization. We expect this technology to transform rapid volumetric production for objects at the nanoscopic to macroscopic length scales.
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http://dx.doi.org/10.1038/s41586-020-3029-7DOI Listing
December 2020

Light-mediated chiroptical switching of an achiral foldamer host in presence of a carbohydrate guest.

Chem Commun (Camb) 2021 Jan;57(1):93-96

Department Pharmazie and Center for Integrated Protein Science, Ludwig-Maximilians-Universität, Butenandtstr. 5-13, 81377 München, Germany.

A photoresponsive diarylethene was incorporated in an achiral helical foldamer container. A carbohydrate guest was found to induce opposite handedness upon binding to the open and closed forms of the diarylethene-containing foldamer, thus enabling chiroptical switching of an achiral host mediated by a chiral guest.
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http://dx.doi.org/10.1039/d0cc06484jDOI Listing
January 2021

Control of long-distance motion of single molecules on a surface.

Science 2020 11;370(6519):957-960

Department of Physical Chemistry, University of Graz, Heinrichstrasse 28, 8010 Graz, Austria.

Spatial control over molecular movement is typically limited because motion at the atomic scale follows stochastic processes. We used scanning tunneling microscopy to bring single molecules into a stable orientation of high translational mobility where they moved along precisely defined tracks. Single dibromoterfluorene molecules moved over large distances of 150 nanometers with extremely high spatial precision of 0.1 angstrom across a silver (111) surface. The electrostatic nature of the effect enabled the selective application of repulsive and attractive forces to send or receive single molecules. The high control allows us to precisely move an individual and specific molecular entity between two separate probes, opening avenues for velocity measurements and thus energy dissipation studies of single molecules in real time during diffusion and collision.
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http://dx.doi.org/10.1126/science.abd0696DOI Listing
November 2020

Tunable Photomechanics in Diarylethene-Driven Liquid Crystal Network Actuators.

ACS Appl Mater Interfaces 2020 Oct 8;12(42):47939-47947. Epub 2020 Oct 8.

Smart Photonic Materials, Faculty of Engineering and Natural Sciences, Tampere University, P.O. Box 541, FI-33101 Tampere, Finland.

The response of soft actuators made of stimuli-responsive materials can be phenomenologically described by a stimulus-deformation curve, depicting the controllability and sensitivity of the actuator system. Manipulating such stimulus-deformation curve allows fabricating soft microrobots with reconfigurable actuation behavior, which is not easily achievable using conventional materials. Here, we report a light-driven actuator based on a liquid crystal polymer network containing diarylethene (DAE) photoswitches as cross-links, in which the stimulus-deformation curve under visible-light illumination is tuned with UV light. The tuning is brought about by the reversible electrocyclization of the DAE units. Because of the excellent thermal stability of the visible-absorbing closed-form DAEs, the absorbance of the actuator can be optically fixed to a desired value, which in turn dictates the efficiency of photothermally induced deformation. We employ the controllability in devising a logical AND gate with macroscopic output, i.e., an actuator that bends negligibly under UV or visible light irradiation, but with profound shape change when addressed to both simultaneously. The results provide design tools for reconfigurable microrobotics and polymer-based logic gating.
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http://dx.doi.org/10.1021/acsami.0c12735DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7586294PMC
October 2020

Graphene transistors for real-time monitoring molecular self-assembly dynamics.

Nat Commun 2020 Sep 18;11(1):4731. Epub 2020 Sep 18.

University of Strasbourg, CNRS, ISIS UMR 7006, 8 allée Gaspard Monge, 67000, Strasbourg, France.

Mastering the dynamics of molecular assembly on surfaces enables the engineering of predictable structural motifs to bestow programmable properties upon target substrates. Yet, monitoring self-assembly in real time on technologically relevant interfaces between a substrate and a solution is challenging, due to experimental complexity of disentangling interfacial from bulk phenomena. Here, we show that graphene devices can be used as highly sensitive detectors to read out the dynamics of molecular self-assembly at the solid/liquid interface in-situ. Irradiation of a photochromic molecule is used to trigger the formation of a metastable self-assembled adlayer on graphene and the dynamics of this process are monitored by tracking the current in the device over time. In perspective, the electrical readout in graphene devices is a diagnostic and highly sensitive means to resolve molecular ensemble dynamics occurring down to the nanosecond time scale, thereby providing a practical and powerful tool to investigate molecular self-organization in 2D.
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http://dx.doi.org/10.1038/s41467-020-18604-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7501237PMC
September 2020

Highly Cooperative Photoswitching in Dihydropyrene Dimers.

Angew Chem Int Ed Engl 2020 Oct 26;59(43):19352-19358. Epub 2020 Aug 26.

Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489, Berlin, Germany.

We present a strategy to achieve highly cooperative photoswitching, where the initial switching event greatly facilitates subsequent switching of the neighboring unit. By linking donor/acceptor substituted dihydropyrenes via suitable π-conjugated bridges, the quantum yield of the second photochemical ring-opening process could be enhanced by more than two orders of magnitude as compared to the first ring-opening. As a result, the intermediate mixed switching state is not detected during photoisomerization although it is formed during the thermal back reaction. Comparing the switching behavior of various dimers, both experimentally and computationally, helped to unravel the crucial role of the bridging moiety connecting both photochromic units. The presented dihydropyrene dimer serves as model system for longer cooperative switching chains, which, in principle, should enable efficient and directional transfer of information along a molecularly defined path. Moreover, our concept allows to enhance the photosensitivity in oligomeric and polymeric systems and materials thereof.
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http://dx.doi.org/10.1002/anie.202008523DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7589249PMC
October 2020

Engineering Optically Switchable Transistors with Improved Performance by Controlling Interactions of Diarylethenes in Polymer Matrices.

J Am Chem Soc 2020 06 11;142(25):11050-11059. Epub 2020 Jun 11.

Université de Strasbourg, CNRS, ISIS, 8 alleé Gaspard Monge, 67000 Strasbourg, France.

The integration of photochromic molecules into semiconducting polymer matrices via blending has recently attracted a great deal of attention, as it provides the means to reversibly modulate the output signal of electronic devices by using light as a remote control. However, the structural and electronic interactions between photochromic molecules and semiconducting polymers are far from being fully understood. Here we perform a comparative investigation by combining two photochromic diarylethene moieties possessing similar energy levels yet different propensity to aggregate with five prototypical polymer semiconductors exhibiting different energy levels and structural order, ranging from amorphous to semicrystalline. Our in-depth photochemical, structural, morphological, and electrical characterization reveals that the photoresponsive behavior of thin-film transistors including polymer/diarylethenes blends as the active layer is governed by a complex interplay between the relative position of the energy levels and the polymer matrix microstructure. By matching the energy levels and optimizing the molecular packing, high-performance optically switchable organic thin-film transistors were fabricated. These findings represent a major step forward in the fabrication of light-responsive organic devices.
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http://dx.doi.org/10.1021/jacs.0c02961DOI Listing
June 2020

Donor-Acceptor Dihydropyrenes Switchable with Near-Infrared Light.

J Am Chem Soc 2020 07 24;142(27):11857-11864. Epub 2020 Jun 24.

Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489 Berlin, Germany.

The use of low-intensity NIR light to operate molecular switches offers several potential advantages including enhanced penetration into bulk materials, in particular biological tissues, and reduced radiation damage due to the limited photon energies. The latter, however, pose a challenge for designing reasonably bistable systems. We have developed a general design strategy for direct one-photon NIR photoswitches based on negative photochromic dihydropyrenes carrying opposing strong donor-acceptor substituents either along the long axis of the molecule or across it. Thus, two series of 2,7- and 4,9-disubstituted dihydropyrenes were synthesized, and their photothermal properties investigated as a function of the type, strength, and position of the attached donor and acceptor substituents as well as the polarity of the environment. By shifting the excitation wavelength deep into the NIR, both NIR one-photon absorption cross-section and photoisomerization efficiency could be maximized while retaining a reasonable thermal stability of the metastable cyclophanediene isomer. Thus, the lowest optical transition was shifted beyond 900 nm, the NIR cross-section was enhanced by two orders of magnitude, and the thermal half-lives vary between milliseconds and hours. These unique features open up ample opportunities for noninvasive, optically addressable materials and material systems.
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http://dx.doi.org/10.1021/jacs.0c04219DOI Listing
July 2020

From Responsive Molecules to Interactive Materials.

Adv Mater 2020 May;32(20):e2000215

DWI - Leibniz Institute for Interactive Materials, Forckenbeckstr. 50, 52056, Aachen, Germany.

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http://dx.doi.org/10.1002/adma.202000215DOI Listing
May 2020

Photomodulation of Charge Transport in All-Semiconducting 2D-1D van der Waals Heterostructures with Suppressed Persistent Photoconductivity Effect.

Adv Mater 2020 Jul 6;32(26):e2001268. Epub 2020 May 6.

University of Strasbourg, CNRS, ISIS UMR 7006, 8 Alleé Gaspard Monge, Strasbourg, F-67000, France.

Van der Waals heterostructures (VDWHs), obtained via the controlled assembly of 2D atomically thin crystals, exhibit unique physicochemical properties, rendering them prototypical building blocks to explore new physics and for applications in optoelectronics. As the emerging alternatives to graphene, monolayer transition metal dichalcogenides and bottom-up synthesized graphene nanoribbons (GNRs) are promising candidates for overcoming the shortcomings of graphene, such as the absence of a bandgap in its electronic structure, which is essential in optoelectronics. Herein, VDWHs comprising GNRs onto monolayer MoS are fabricated. Field-effect transistors (FETs) based on such VDWHs show an efficient suppression of the persistent photoconductivity typical of MoS , resulting from the interfacial charge transfer process. The MoS -GNR FETs exhibit drastically reduced hysteresis and more stable behavior in the transfer characteristics, which is a prerequisite for the further photomodulation of charge transport behavior within the MoS -GNR VDWHs. The physisorption of photochromic molecules onto the MoS -GNR VDWHs enables reversible light-driven control over charge transport. In particular, the drain current of the MoS -GNR FET can be photomodulated by 52%, without displaying significant fatigue over at least 10 cycles. Moreover, four distinguishable output current levels can be achieved, demonstrating the great potential of MoS -GNR VDWHs for multilevel memory devices.
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http://dx.doi.org/10.1002/adma.202001268DOI Listing
July 2020

Mechanistic Insights into the Triplet Sensitized Photochromism of Diarylethenes.

Chemistry 2020 Jun 26;26(34):7672-7677. Epub 2020 May 26.

Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489, Berlin, Germany.

Operating photoswitchable molecules repetitively and reliably is crucial for most of their applications, in particular in (opto)electronic devices, and related to reversibility and fatigue resistance, which both critically depend on the photoisomerization mechanism defined by the substitution pattern. Two diarylethene photoswitches bearing biacetyl triplet sensitizers either at the periphery or at the core were investigated using both stationary as well as transient UV/Vis absorption spectroscopy ranging from the femtosecond to the microsecond time scale. The diarylethene with two biacetyl moieties at the periphery is switching predominantly from the triplet excited state, giving rise to an enhanced fatigue resistance. In contrast, the diarylethene bearing one diketone at the photoreactive inner carbon atom cyclizes from the singlet excited state and shows significantly higher quantum yields for both cyclization and cycloreversion.
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http://dx.doi.org/10.1002/chem.202000877DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7318355PMC
June 2020

Site-Specific Conjugation of Native Antibodies Using Engineered Microbial Transglutaminases.

Bioconjug Chem 2020 04 12;31(4):1070-1076. Epub 2020 Mar 12.

Merck KGaA, Frankfurter Str. 250, 64293 Darmstadt, Germany.

Site-specific bioconjugation technologies are frequently employed to generate homogeneous antibody-drug conjugates (ADCs) and are generally considered superior to stochastic approaches like lysine coupling. However, most of the technologies developed so far require undesired manipulation of the antibody sequence or its glycan structures. Herein, we report the successful engineering of microbial transglutaminase enabling efficient, site-specific conjugation of drug-linker constructs to position HC-Q295 of native, fully glycosylated IgG-type antibodies. ADCs generated via this approach demonstrate excellent stability as well as strong efficacy and . As it employs different drug-linker structures and several native antibodies, our study additionally proves the broad applicability of this approach.
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http://dx.doi.org/10.1021/acs.bioconjchem.0c00061DOI Listing
April 2020

Modulating the luminance of organic light-emitting diodes via optical stimulation of a photochromic molecular monolayer at transparent oxide electrode.

Nanoscale 2020 Mar;12(9):5444-5451

University College London, Department Physics and Astronomy and London Centre for Nanotechnology, London WC1H 0AH, UK.

Self-assembled monolayers (SAMs) deposited on bottom electrodes are commonly used to tune charge carrier injection or blocking in optoelectronic devices. Beside the enhancement of device performance, the fabrication of multifunctional devices in which the output can be modulated by multiple external stimuli remains a challenging target. In this work, we report the functionalization of an indium tin oxide (ITO) electrode with a SAM of a diarylethene derivative designed for optically control the electronic properties. Following the demonstration of dense SAM formation and its photochromic activity, as a proof-of-principle, an organic light-emitting diode (OLED) embedding the light-responsive SAM-covered electrode was fabricated and characterized. Optically addressing the two-terminal device by irradiation with ultraviolet light doubles the electroluminescence. The original value can be restored reversibly by irradiation with visible light. This expanded functionality is based on the photoinduced modulation of the electronic structure of the diarylethene isomers, which impact the charge carriers' confinement within the emissive layer. This approach could be successfully exploited in the field of opto-communication technology, for example to fabricate opto-electronic logic circuits.
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http://dx.doi.org/10.1039/d0nr00724bDOI Listing
March 2020

Covalent on-surface polymerization.

Nat Chem 2020 02 29;12(2):115-130. Epub 2020 Jan 29.

Department of Chemistry, Humboldt-Universität zu Berlin, Berlin, Germany.

With the rapid development of scanning probe microscopy, it has become possible to study polymerization processes on suitable surfaces at the atomic level and in real space. In the two-dimensional confinement of a surface, polymerization reactions can give rise to the formation of unprecedented polymers with unique structures and properties, not accessible in solution. After a little over one decade since the discovery of covalent on-surface polymerization, we give an overview of the field, analyse the crucial aspects and critically reflect on the status quo. Specifically, we provide some general considerations about fundamental mechanisms as well as kinetics and thermodynamics of on-surface polymerization processes. The important role of the surface is detailed in view of its ability to control polymer formation with regard to structure, dimensionality and composition. Furthermore, examples that allow for locally induced polymerization are highlighted. Finally, we provide an analysis of scientific challenges in the field and outline future prospects.
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http://dx.doi.org/10.1038/s41557-019-0392-9DOI Listing
February 2020

Simultaneous Optical Tuning of Hole and Electron Transport in Ambipolar WSe Interfaced with a Bicomponent Photochromic Layer: From High-Mobility Transistors to Flexible Multilevel Memories.

Adv Mater 2020 Mar 24;32(11):e1907903. Epub 2020 Jan 24.

University of Strasbourg, CNRS, ISIS UMR 7006, 8 Alleé Gaspard Monge, F-67000, Strasbourg, France.

The interfacing of 2D materials (2DMs) with photochromic molecules provides an efficient solution to reversibly modulate their outstanding electronic properties and offers a versatile platform for the development of multifunctional field-effect transistors (FETs). Herein, optically switchable multilevel high-mobility FETs based on few-layer ambipolar WSe are realized by applying on its surface a suitably designed bicomponent diarylethene (DAE) blend, in which both hole and electron transport can be simultaneously modulated for over 20 cycles. The high output current modulation efficiency (97% for holes and 52% for electrons) ensures 128 distinct current levels, corresponding to a data storage capacity of 7 bit. The device is also implemented on a flexible and transparent poly(ethylene terephthalate) substrate, rendering 2DM/DAE hybrid structures promising candidates for flexible multilevel nonvolatile memories.
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http://dx.doi.org/10.1002/adma.201907903DOI Listing
March 2020

Enlightening Materials with Photoswitches.

Adv Mater 2020 May 24;32(20):e1905966. Epub 2020 Jan 24.

Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, 12489, Berlin, Germany.

Incorporating molecular photoswitches into various materials provides unique opportunities for controlling their properties and functions with high spatiotemporal resolution using remote optical stimuli. The great and largely still untapped potential of these photoresponsive systems has not yet been fully exploited due to the fundamental challenges in harnessing geometrical and electronic changes on the molecular level to modulate macroscopic and bulk material properties. Herein, progress made during the past decade in the field of photoswitchable materials is highlighted. After pointing to some general design principles, materials with an increasing order of the integrated photoswitchable units are discussed, spanning the range from amorphous settings over surfaces/interfaces and supramolecular ensembles, to liquid crystalline and crystalline phases. Finally, some potential future directions are pointed out in the conclusion. In view of the exciting recent achievements in the field, the future emergence and further development of light-driven and optically programmable (inter)active materials and systems are eagerly anticipated.
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http://dx.doi.org/10.1002/adma.201905966DOI Listing
May 2020

Multivalency in Heteroternary Complexes on Cucurbit[8]uril-Functionalized Surfaces: Self-assembly, Patterning, and Exchange Processes.

Chempluschem 2019 09 12;84(9):1324-1330. Epub 2019 Jun 12.

Molecular Nanofabrication Group, MESA+ Institute for Nanotechnology, Department of Science and Technology, University of Twente, P.O. Box 217, 7500, AE Enschede, The Netherlands.

The spatial confinement of multivalent azopyridine guest molecules mediated by cucurbit[8]urils is described. Fluorescent dye-labelled multivalent azopyridine molecules were attached to preformed methyl viologen/cucurbit[8]uril inclusion complexes in solution and at surfaces. The formation of the resulting heteroternary host-guest complexes was verified in solution and on gold substrates. Surface binding constants of the multivalent ligands were two orders of magnitude higher than that of the monovalent one. Poly-l-lysine grafted with oligo(ethylene glycol) and maleimide moieties was deposited on cyclic olefin polymer surfaces and further modified with thiolated methyl viologen and cucurbit[8]uril. Defined micrometer-sized patterns were created by soft lithographic techniques. Supramolecular exchange experiments were performed on these surface-bound heterocomplexes, which allowed the creation of cross-patterns by taking advantage of the molecular valency, which led to the substitution of the monovalent guest by the multivalent guests but not vice versa.
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http://dx.doi.org/10.1002/cplu.201900181DOI Listing
September 2019

Shining a Light on Proteolysis Targeting Chimeras.

ACS Cent Sci 2019 Oct 3;5(10):1645-1647. Epub 2019 Oct 3.

Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany.

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http://dx.doi.org/10.1021/acscentsci.9b00955DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6813547PMC
October 2019

Isolation of Anti-Hapten Antibodies by Fluorescence-Activated Cell Sorting of Yeast-Displayed B-Cell Receptor Gene Repertoires.

Methods Mol Biol 2020 ;2070:267-287

Antibody-Drug Conjugates and Targeted NBE Therapeutics, Merck KGaA, Darmstadt, Germany.

Anti-hapten antibodies are widely used as specific immunochemical detection tools in a variety of clinical and environmental analyses. The sensitivity, however, is limited due to the resulting antibody affinities to the haptens which, in turn, leads to a high demand for specific affinity reagents. A well-established path for the generation of high-affinity antibodies is the immunization of animals with the target antigen. However, the generation of anti-hapten antibodies via immunization remains challenging as small molecule haptens usually possess low immunogenicity and, therefore, must be coupled to an immunogenic and high molecular weight carrier to provoke an immune response.Consequently, antibodies are primarily raised against the carrier molecule or structural features of the hapten-linker fused to the carrier protein. This turns the generation of antibodies which bind exclusively to the hapten structure into a search for the needle in a haystack. In the following chapter, we describe how yeast surface display and high-throughput fluorescence-activated cell sorting can be used to isolate anti-hapten antibodies from a large, yeast-displayed B-cell receptor gene library derived from immunized animals. For this, we describe in detail the preparation of protein-hapten conjugates, the immunization procedure, and the subsequent screening process. Moreover, we provide a simple flow cytometry protocol that allows for a rapid analysis of the enriched clones toward free hapten binding.
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http://dx.doi.org/10.1007/978-1-4939-9853-1_15DOI Listing
December 2020

Modulating the Charge Transport in 2D Semiconductors via Energy-Level Phototuning.

Adv Mater 2019 Sep 12;31(39):e1903402. Epub 2019 Aug 12.

University of Strasbourg, CNRS, ISIS UMR 7006, 8 Alleé Gaspard Monge, F-67000, Strasbourg, France.

The controlled functionalization of semiconducting 2D materials (2DMs) with photoresponsive molecules enables the generation of novel hybrid structures as active components for the fabrication of high-performance multifunctional field-effect transistors (FETs) and memories. This study reports the realization of optically switchable FETs by decorating the surface of the semiconducting 2DMs such as WSe and black phosphorus with suitably designed diarylethene (DAE) molecules to modulate their electron and hole transport, respectively, without sacrificing their pristine electrical performance. The efficient and reversible photochemical isomerization of the DAEs between the open and the closed isomer, featuring different energy levels, makes it possible to generate photoswitchable charge trapping levels, resulting in the tuning of charge transport through the 2DMs by alternating illumination with UV and visible light. The device reveals excellent data-retention capacity combined with multiple and well-distinguished accessible current levels, paving the way for its use as an active element in multilevel memories.
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http://dx.doi.org/10.1002/adma.201903402DOI Listing
September 2019

Modulating Guest Uptake in Core-Shell MOFs with Visible Light.

Angew Chem Int Ed Engl 2019 Sep 26;58(37):12862-12867. Epub 2019 Jul 26.

Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor Strasse 2, 12489, Berlin, Germany.

A two-component core-shell UiO-68 type metal-organic framework (MOF) with a nonfunctionalized interior for efficient guest uptake and storage and a thin light-responsive outer shell was prepared by initial solvothermal MOF synthesis followed by solvent-assisted linker exchange. The bulky shell linker features two tetra-ortho-fluorinated azobenzene moieties to exploit their advantageous photoisomerization properties. The obtained perfect octahedral MOF single crystals can be switched repeatedly and with an unprecedented efficiency between E- and Z-rich states using visible light only. Due to the high photoswitch density per pore of the shell layer, its steric demand and thus molecular uptake (and release) can be conveniently modulated upon green and blue light irradiation. Therefore, the "smart" shell acts as a light-controlled kinetic barrier or "gate" for the diffusion of cargo molecules in and out of the MOF crystals.
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http://dx.doi.org/10.1002/anie.201906606DOI Listing
September 2019

Regorafenib Is Associated With Increased Skeletal Muscle Loss Compared to TAS-102 in Metastatic Colorectal Cancer.

Clin Colorectal Cancer 2019 06 11;18(2):159-166.e3. Epub 2019 Apr 11.

Department of Internal Medicine III with Haematology, Medical Oncology, Haemostaseology, Infectiology, and Rheumatology, Oncologic Center, Salzburg Cancer Research Institute, Laboratory for Immunological and Molecular Cancer Research (SCRI-LIMCR), Paracelsus Medical University Salzburg, Salzburg, Austria. Electronic address:

Background: Current guidelines of the National Comprehensive Cancer Network and the European Society of Medical Oncology recommend regorafenib or trifluridine/tipiracil (TAS-102) for third-line therapy of metastatic colorectal cancer (mCRC). We evaluated the impact of regorafenib and TAS-102 treatment on skeletal muscle dynamics and sarcopenia.

Patients And Methods: This retrospective analysis was based on unselected, consecutive mCRC patients treated with regorafenib and/or TAS-102 during third or later line of therapy at our tertiary-care cancer center in Salzburg, Austria. The skeletal muscle index (SMI, cm/m) and sarcopenia were evaluated from cross-sectional computed tomographic images at the level of the third lumbar vertebra.

Results: Between January 2013 and April 2018, a total of 45 patients had received regorafenib and/or TAS-102. At initial mCRC diagnosis and at initiation of third-line therapy, 24% and 54% of patients presented with sarcopenia. A statistically significant skeletal muscle loss was observed during regorafenib treatment (median SMI change: -2.75 cm/m [-6.3%]; P < .0001), which was not the case during TAS-102 therapy (-1.5 cm/m [-3.5%]; P = .575). Furthermore, subclassification of patients into 3 groups-normal muscle mass, stable sarcopenia, and new-onset sarcopenia-at initiation of third-line therapy permitted discrimination of overall survival, with 1-year overall survival rates of 61%, 29%, and 16%, respectively (P = .04).

Conclusion: The frequency of sarcopenia increases during the course of mCRC and negatively affects survival. In contrast to TAS-102, regorafenib is associated with increased skeletal muscle loss during mCRC treatment and should therefore be used with caution in mCRC patients with preexisting sarcopenia or a history of recent weight loss.
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http://dx.doi.org/10.1016/j.clcc.2019.04.003DOI Listing
June 2019

Indexing grazing-incidence X-ray diffraction patterns of thin films: lattices of higher symmetry.

J Appl Crystallogr 2019 Apr 1;52(Pt 2):428-439. Epub 2019 Apr 1.

Department of Physics, Department of Chemistry and Biochemistry, Centre for Research in Molecular Modeling (CERMM), Centre for Nanoscience Research (CeNSR), Concordia University, 7141 Sherbrooke Street W., SP 265-20, Montreal, Quebec, Canada H4B 1R6.

Grazing-incidence X-ray diffraction studies on organic thin films are often performed on systems showing fibre-textured growth. However, indexing their experimental diffraction patterns is generally challenging, especially if low-symmetry lattices are involved. Recently, analytical mathematical expressions for indexing experimental diffraction patterns of triclinic lattices were provided. In the present work, the corresponding formalism for crystal lattices of higher symmetry is given and procedures for applying these equations for indexing experimental data are described. Two examples are presented to demonstrate the feasibility of the indexing method. For layered crystals of the prototypical organic semiconductors di-indeno-perylene and (-di-fluoro)-sexi-phenyl, as grown on highly oriented pyrolytic graphite, their yet unknown unit-cell parameters are determined and their crystallographic lattices are identified as monoclinic and orthorhombic, respectively.
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http://dx.doi.org/10.1107/S1600576719003029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6448685PMC
April 2019

Photoswitchable polymerization catalysis: state of the art, challenges, and perspectives.

Chem Commun (Camb) 2019 Apr;55(30):4290-4298

Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.

Adjusting the length, composition, and microstructure of a polymer during the process of its formation in principle allows achieving the desired properties, thereby enabling custom-design of the thus generated polymer for its targeted function. Over the past years, different stimuli have been applied to manipulate responsive catalyst systems in situ; among them light takes center stage as perhaps the most promising stimulus. Here, we highlight recent progress in the area of photoswitchable polymerization catalysis. In particular, we focus on the challenge of combining photoswitchable and catalytically active units in a manner that both entities are somehow coupled and interact, yet also retaining their switching and catalysis functions under suitable conditions. We introduce the requirements for an ideal case of a photoswitchable polymerization catalyst system and use them to analyze the current state of the art. Based on our analysis of the status quo, we point to scientific challenges in the field and sketch perspectives including potential applications.
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http://dx.doi.org/10.1039/c9cc01431dDOI Listing
April 2019