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News Archive 2015-2018

December 15th, New paper in ACS NANO online!

In collaboration with the groups of Prof. Doreen Mollenhauer and Prof. André Schirmeisen a new paper "Adsorption Structure of Mono- and Diradicals on a Cu(111) Surface: Chemoselective Dehalogenation of 4-Bromo-3″-iodo-p-terphenyl" was published online. The investigation demonstrates the potential of selective dehalogenation using bond imaging atomic force microscopy with CO-functionalized tips.

The deiodination and debromination reactions are triggered either by heating or by locally applying voltage pulses with the tip. We observed a strong hierarchical behavior of the dehalogenation with respect to temperature and voltage. In connection with first-principles simulations we can determine the orientation and position of the pristine molecules as well as adsorbed mono/diradicals and the halogens. We find that the isolated radicals are chemisorbed to Cu(111) top sites, which are lifted by 16 pm (meta-position) and 32 pm (para-position) from the Cu surface plane. This leads to a strongly twisted and bent 3D adsorption structure. After heating, different types of dimers are observed whose molecules are either bound to surface atoms or connected via Cu adatoms. Such knowledge about the intermediate geometry and its interaction with the surface will open the way to rationally design syntheses on surfaces. DOI: 10.1021/acsnano.8b06283

ACS_NANO-2018-062833_0010.gif

August 8th, Opening of Art Exhibition "Perspektivisomorphe".

The Exhibition originated from an interdisciplinary collaboration of the Art & Chemistry departements of the JLU. The concept of the central perspective is transfered to chemistry to develop new graphical representations for molecules and atoms. The project is supported by the Schering Stiftung.

The interdisciplinary research project was designed by Prof. Dr. Ansgar Schnurr (Institute for Art Education), Prof. Dr. Hermann Wegner (Institute for Organic Chemistry), and Jannis Neumann (student of art education and biology), Justus Liebig University (JLU) Giessen.

Sketches from the artists Patrick Borchers, Jette Flügge, and Christoph Kern are presented. Visting the exhibition will be possible until october, 14th from 8.30 am  until 11.00 pm at the central library of the university Giessen.

Further information concerning the exhibition is online available at the Giessener Anzeiger or the hompage of the Schering Stiftung.

June 19th, Wegner Group awarded with Safety Prize 2018

The Safety prize 2018 of the Justus-Liebig university and the Unfallkasse Hessen was awarded to the Wegner group for obtaining the highest score in the annual safety inspection.

In a ceremony held at the university's main building, JLU-president Prof. Dr. Joybrato Mukherjee handed over the award, which is also supported by the Unfallkasse Hessen, to Prof. Hermann A. Wegner and the members of his group. The prize shall reward the commitment of all members of the group for maintaining a high safety level in everydays laboratory research.

Arbeitssicherheitspreis_Friese_01.jpg

Foto: JLU-Pressestelle / Katrina Friese

May 2nd, Two new publications online available!

Another publication in Angewandte Chemie Int. Ed. with the title "Electronic communication between two [10]cycloparaphenylenes and bisazafullerene (C59N)2 induced by cooperative complexation" with Nikos Tagmatarchis and Chris Ewels was recently published online. Also another paper "Lattice Mismatch Drives Spatial Modulation of Corannulene Tilt on Ag(111)" is now online available.

 

For the first publication, a complex of [10]cycloparaphenylene ([10]CPP) with bisazafullerene (C59N)2 was investigated experimentally and computationally. Two [10]CPP rings are bound to the dimeric azafullerene giving [10]CPP⊃(C59N)2⊂[10]CPP. Photophysical and redox properties support an electronic interaction between the components especially with the second [10]CPP bound. Unlike [10]CPP⊃C60, where there is negligible electronic communication between the two species, upon photoexcitation a partial charge transfer phenomenon was revealed between [10]CPP and (C59N)2 reminiscent of CPP encapsulated metallofullerenes. Such an alternative electron‐rich fullerene species demonstrates C60‐like ground‐state properties and metallofullerene‐like excited‐state properties opening new avenues for construction of functional supramolecular architectures with organic materials.

DOI: 10.1002/anie.201713197

 

In second publication the adsorption of corannulene (C20H10) on the Ag(111) surface by experimental and simulated scanning tunneling microscopy (STM), X-ray photoemission (XPS) and near-edge X-ray absorption fine structure (NEXAFS) was investigated. Structural optimizations of the adsorbed molecules were performed by density functional theory (DFT) and the core excited spectra evaluated within the transition potential approach. Corannulene is physisorbed in a bowl-up orientation displaying a very high mobility (diffusing) and dynamics (tilting and spinning) at room temperature. At the monolayer saturation coverage, molecules order into a close compact phase with an average intermolecular spacing of ∼10.5±0.5Å. The lattice mismatch drives a long wavelength structural modulation of the molecular rows, which, however, could not be identified with a specific superlattice periodicity. DFT calculations indicate that the structural and spectroscopic properties are intermediate between those predicted for the limiting cases of an on-hexagon geometry (with a three-fold, ∼8.6Å unit mesh) and an on-pentagon (with a four-fold,∼11.5Å unit mesh). We suggest that molecules smoothly change their equilibrium configuration along the observed long wavelength modulation of the molecular rows by varying their tilt and azimuth in between the geometric constraints calculated for molecules in the three-fold and four-fold phases.

DOI: 10.1021/acs.jpcc.7b11581

March 14th, air stable catalyst for inverse electron-demand Diels–Alder reaction.

We report an air-stable bisboron complex as an efficient catalyst for the inverse electron-demand Diels–Alder (IEDDA) reaction of 1,2-diazine as well as 1,2,4,5-tetrazine.

Its stability towards air and moisture was demonstrated by NMR studies enabling its application in organic transformations without glovebox. A one-pot procedure for its synthesis was developed starting from 1,2-bis(trimethylsilyl)benzene greatly enhancing its practicality. Comparative reactions were carried out to evaluate its catalytic activity in IEDDA reactions of diazine including phthalazine as well as 1,2,4,5-tetrazine.

DOI: 10.3762/bjoc.14.48

January 26th, First Paper in 2018 accepted.

A new paper with the title "The Quest for Organic Active Materials for Redox Flow Batteries: 2,3‑Diaza-anthraquinones and their Electrochemical Properties" which explores the use of diaza-anthraquinones in redox flow systems was just accepted for publication. This investigation was done in collaboration by with the groups of Prof. Jürgen Janek and Prof. Doreen Mollenhauer.

To be competitive with other electrically rechargeable large scale energy storages, the range of active materials for redox flow batteries is currently expanded by organic compounds – this holds especially for the redox active material class of quinones that can be derived from naturally abundant resources at low cost. Here we propose the modified quinone 2,3-diaza-anthracenedione, and two of its derivatives, as promising active material for aqueous redox flow batteries. We systematically study the electrochemical performance (redox potentials, rate constants, diffusion coefficients) for these three compounds at different pH value experimentally and complement the results with density functional calculations: A positive redox potential shift of about 300 mV is achieved by the incorporation of a diaza moiety into the anthraquinone base structure. Our experiments at low pH show that the addition of a methoxy group to the base structure of the 2,3-diaza-anthracenedione strongly increases the electrochemical stability in aqueous acidic media – although the impact of the conjugate base is not clear yet. Furthermore, a functionalization with two hydroxyl groups evokes a negative redox potential shift of 54 mV in acidic and 264 mV in alkaline solution. This demonstrates that this novel class of compounds is very versatile and can be tailor-made for the use as active material in redox flow batteries – either in alkaline or acidic media. The 2,3-diaza-anthracenediones presented in this study were used as anolyte active materials in a full redox flow cell as a proof of concept; best cycling stability was achieved with 2,3-diaza-anthracenediones functionalized with a methoxy group as active material. Transferring our findings to other quinone base structures, such as naphtoquinones, could lead to even better performing catholyte and anolyte active materials for future redox flow batteries with organic active material.

DOI: 10.1021/acs.chemmater.7b04220

December 20th, New paper in JACS online!

In our new paper "Stable Organic Neutral Diradical via Reversible Coordination", we report the formation of a stable neutral diboron diradical simply by coordination of an aromatic dinitrogen compound to an ortho-phenyldiborane. Computations were performed in collaboration with the group of professor Peter R. Schreiner.

This process of coordination is reversible upon addition of pyridine. The diradical species is stable above 200 °C. Computations are consistent with an open-shell triplet diradical with a very small open-shell singlet−triplet energy gap that is indicative of the electronic disjointness of the two radical sites. This opens a new way of generating stable radicals with fascinating electronic properties useful for a large variety of applications. The paper is now online available.

BN_diradical

June 12th, New paper in Chem. Phys. Chem. accepted.

A new paper published in collaboration with the groups of Andreas Dreuw and Josef Wachtveitl with the title "Ultrafast excited-state deactivation dynamics of cyclotrisazobenzene - a novel type of UV-B absorber" is now online available.

This work provides a deeper insight into the photoisomerization reaction of a cyclic azobenzene. We present here a combined experimental and theoretical study on the ultrafast dynamics of cyclotrisazobenzene (CTA) and demonstrate that the structural constraints in CTA prevent isomerization of the photoswitch units. In the developed molecular picture, the N=N bonds respond elastically to the motion along the isomerization coordinates, which leads to ultrafast and complete dissipation of the UV excitation as heat. Based on this property, CTA and possibly other similarly designed molecules can be utilized as UV-absorbers for example in sunscreens; other potential applications are also envisioned.

Azo_UV_absorber

June 7th, New co-worker and bachelor students welcome!

The Wegner group welcomes its new co-worker Sebastian Beeck, who started his PhD studies in the field of Boron based Lewis acid catalysis after successfully finishing his master thesis on cycloparaphenylenes.

Furthermore, we like to welcome our new bachelor candidates Anne, Larissa and Daniel. We hope, that you will enjoy your time in the Wegner group.

May 4th, Publication in Synthesis available!

The first publication of Andreas Heindl in Synthesis is now online available. In this report a macrocyclic bisazobenzene is presented that exists as the stable Z-isomer.

Azobenzenes have attracted increasing attention in the past years due to their application as molecular switches. The synthetic efforts for a macrocyclic bisazobenzene as well as the successful strategy are discussed. Final ring closure under continuous irradiation gave the (Z,Z)-bisazobenzenophane. This Z-azobenzene does not show any isomerization under either heating or prolonged irradiation. The thermal stability of the Z-form has also been supported by computations. The prepared bisazobenzenophane represents one of the few azobenzenes in which the Z-isomer is more stable than the E-isomer.

z-stable_azobenzene_macrocycle.gif

May 3rd, New Paper in Appl. Phys. Lett. online!

The publication "Chemical bond imaging using higher eigenmodes of tuning fork sensors in atomic force microscopy" demonstrates the ability of resolving the chemical structure of single organic molecules using non-contact atomic force microscopy with submolecular resolution.

April 28th, Goodbye Zhenpin!

Zhenpin Lu obtained his doctoral degree after beginning his PhD in June 2013.

The Wegner group would like to congratulate Zhenpin Lu to his doctoral degree. We hope you had a nice time in the Wegner group and that you will be able to continue your successful work in the Nitschke group in Cambridge. We wish you all the best for your future.

April 13th, Paper in Organic Chemistry Frontiers published!

A new methodology to generate 2,3-diaza-anthraquinones and anthraquinones starting from 1,2,4,5-tetrazine via a bidentate bisborane Lewis acid catalysed inverse electron-demand Diels–Alder (IEDDA) reaction is presented.

The synthesis of 2,3-diaza-anthraquinones by an IEDDA reaction of 1,4-naphthoquinones (1,4-NQs) with 1,2,4,5-tetrazine (TZ) as the nitrogen source has been developed. Only due to the coordination of TZ with the bisborane catalyst, the IEDDA reaction of electron-deficient 1,4-NQs is possible. The 2,3-DAAQs themselves are suitable dienes for a second bidentate Lewis acid catalysed IEDDA reaction with various dienophiles to afford substituted anthraquinones. Anthraquinones have been discussed as privileged structures for applications in medicinal as well as materials science.

tetrazine_IEDDA_azaantrachinone.jpg

March 28th, New Paper in ACS Nano online available!

The paper with the title "Imaging Successive Intermediate States of the On-Surface Ullmann Reaction on Cu(111): Role of the Metal Coordination" shows a nice application of atomic force microscopy with submolecular resolution to study the complete reaction pathway of the Ullmann-type coupling on a Cu surface.

March 8th, New Synlett account online!

A new Synlett account by Sebastian Beeck et al. with the Title "Where Are They Now? Aromaticity as a Source for Strain Energy? Synthesis of Curved Polycyclic Aromatic Structures via [2+2+2] Cycloaddition Reactions" is now available online as eFirst paper.

The article describes synthetic approaches for curved polycyclic aromatics such as circulenes, helicenes and cycloparaphenylenes by using a [2+2+2] cycloaddition. Several examples with optimized reaction conditions are shown to help obtaining a better understanding of the process. The online article can be accesed using this hyperlink.

November 30th, Interdisciplinary Discussion by the ZMI

On december 2nd starting at 9 am, the centre for media and interactivity (ZMI) will hold a meeting on the subject of migration. Many different experts are going to discuss pictures about migration with their specific academic background. Together with professor Dr. Ansgar Schnurr, professor Wegner will talk about "Perspektiven_Ordnung_Chaos" starting at 11:45 h in the Margarete-Bieber-Saal in Ludwigstraße 34.

October 15th, New Collaboration with Prof. Ansgar Schnurr

A collaborative project together with Prof. Ansgar Schnurr from Institut für Kunstdidaktik of the JLU on “perspective isomorphs” has been funded by the Ernst-Schering Foundation. In this project the importance of perspective in Art and Chemistry is explored.

August 22nd, New Apprentice Elena

The Wegner group welcomes their new Apprentice Elena.

August 10th, New Paper in Chem. Eur. J. online

The new paper with the title "Bis-Boron Compounds in Catalysis: Bidentate and Bifunctional Activation" gives a nice overview of the great potential of bis-boron compounds in metal-free catalysis.

The article by Luca Schweighauser and Hermann Wegner provides a nice insight into the range of applications provided by utilizing bidentate interactions in Diels–Alder reactions, carbon dioxide reduction, and ammonia-borane dehydrogenation.

June 22nd, Front Cover in Phys. Chem. Chem. Phys.

In cooperation with the groups of Prof. Dr. Josef Wachtveitl (Uni Frankfurt) and Prof. Dr. Andreas Dreuw (Uni Heidelberg), we published a paper on ultrafast isomerization dynamics of different connected bisazobenzene photoswitches in Physical Chemistry Chemical Physics, for which we were chosen to provide the front cover for this issue.

The new paper with the title "Connectivity matters - ultrafast isomerization dynamics of bisazobenzene photoswitches" showing the dependence of the excited state lifetimes on the degree of conjugation in the  multiphotochromic system of bisazobenzene derivatives is available online.

June 20th, Welcome new Liebig-College fellows

The Wegner group welcomes our two new Liebig-College fellows Andrey Petrov and Aleksandra Michalak who will stay for 2-3 months. We hope you will enjoy your time in Giessen and discover not only highlights in chemistry but also in Germany.

March 24th, New Paper in Phys. Chem. Chem. Phys. online

In cooperation with the groups of Prof. Dr. Josef Wachtveitl (Uni Frankfurt) and Prof. Dr. Andreas Dreuw (Uni Heidelberg), we published a new paper on ultrafast isomerization dynamics of different connected bisazobenzene photoswitches, which is now online available at Physical Chemistry Chemical Physics.

The new paper with the title "Connectivity matters - ultrafast isomerization dynamics of bisazobenzene photoswitches" showing the dependence of the excited state lifetimes on the degree of conjugation in the  multiphotochromic system of bisazobenzene derivatives is from now on available online.

 

PCCP_ultrafast_photoswitches

March, 7th, New paper in Org. Lett. online

Luca's, Ina's and Simon's paper about Bidentate Lewis Acid Catalyzed Domino Diels-Alder Reaction of Phthalazine is now online available at Organic Letters.

A new paper with the title "Bidentate Lewis Acid Catalyzed Domino Diels-Alder Reaction of Phthalazine for the Synthesis of Bridged Oligocyclic Tetrahydronaphthalenes" showing a domino process consisting of an inverse and a normal electron demand Diels-Alder reaction to form bridged tri- and tetracyclic 1,2,3,4-tetrahydronaphthalenes  is from now on available online.

tandem_DA_Figure_OrgLett2016.jpg

February 18th, The Wegner group welcomes new Postdoc

Longcheng Hong from China just started his work in the Wegner group.

The Wegner group would like to welcome our new postdoc who will be working on Boron catalyzed Diels Alder reactions and investigate Molecular Structure-Properties Relationship in electronic chemistry.

January 8th, New paper in J. Phys. Chem. C accepted

A new paper in colaboration with the group of Prof. Dr. André Schirmeisen of the Institute of Applied Physics of the JLU was just accepted.

The article with the title "Subsurface Controlled Angular Rotation: Triphenylene Molecules on Au(111) Substrates" is now online available at the Journal of Physical Chemistry C.

October 29th, New PhD and Postdoc Positions available

A new PhD position is available for application with a focus on synthesis and characterisation of organic compounds.

We are pleased to inform you about new Job Offers in the Wegner group. In cooperation with the Janek group, there is a new PhD position available in our group for the synthesis and electrochemical characterisation of substituted aromatic systems especially quinones. For further details, please visit the JLU job market.

 

For a PostDoc position in the Wegner group, please apply directly to Professor Dr.  Hermann A. Wegner.

October 14th, Winners of Young Chemist Award 2015

The three winners of this year's Young Chemist Award are Christina Menzel, Christian Kummer und Larissa-Sophia Blecker who were able to succeed against more than 40 other participants.

The Young Chemist Award at the chemical instituts of the Justus Liebig university Giessen offers high school students the chance to listen to lectures, solve tasks and work in a chemical laboratory. The program covers basic chemical knowledge and trains laboratory skills. After the first round of the award, some participants are selected by an exam for the second round which takes place around august/september. For more detailed information follow this link: Young Chemist Award 2016.

 

An article about the winners of this year can be found in the Giessener Allgemeine Zeitung.

October 6th, Two Master students starting internship

André Blößer and Andreas Heindl startet their master internships in the Wegner group.

With the beginning of the new semester, André Blößer will be working on domino-type Diels-Alder reactions. Andreas Heindl's task is to synthesize oligoazobenzophanes and the investigation of their properties.

September 29th, New paper in Angew. Chem. Int. Ed.

Zhenpin Lu's paper about a bisborane Lewis acid catalyzed release of hydrogen from ammonia borane will soon be available in Angewandte Chemie International Edition.

We congratulate Zhenpin Lu that his paper "Metal-free ammonia borane dehydrogenation catalyzed by a bisborane Lewis acid" was recently accepted by the Angewandte Chemie Int. Ed. and we are looking forward to its publication.

TOC-_ammoniaborane_hydrogen_release.jpg

September 18th, Wegner group moved to a new location

The Wegner group has finally moved in their new Labs at Heinrich Buff Ring 17.

Starting from september 18th, 2015, the Wegner group is now located in the new chemistry building of the Justus Liebig university giessen. The new rooms of the group are located on the upper second floor in building part B ranging from number 228 to 233.

 

Adress:

Institut Organische Chemie 
Prof. Dr. Hermann A. Wegner
Heinrich-Buff-Ring 17
D-35392 Giessen 
Room B 229, 2. Floor

 

 

September 10th, New paper in Angewandte Chemie Int. Ed. online

Luca's, Marcel's and Silvia's paper about London Dispersion interactions in azobenzene isomerization is now online available at Angew. Chem. Int. Ed..

A new paper with the title "Attraction or Repulsion? London Dispersion Forces Control Azobenzene Switches" dealing with the influence of bulky electronically neutral alkyl residues on the cis-trans isomerization rates of azobenzenes is from now on available online in an english and a german version. 

London_dispersion_azobenzene

June 30th, Interdisciplinary PhD Project (IPhD)

The X-Letter 30 (May 2015) by the SystemsX.ch presents an interdisciplinary PhD project, which was successfully finished in the Wegner group.

Silvia Belloto took part in an interdisciplinary PhD project at the EPF Lausanne and the Justus Liebig University Giessen with the title "Quantifying the activity contribution of individual matrix metalloproteinases (MMPs) to the overall MPP activity in the extracellular space using highly specific and photo-switchable inhibitors". This project was supervised by Prof. Christian Heinis, Laboratory of Therapeutic Proteins and Peptides, EPF Lausanne and Prof. Hermann A. Wegner, Institute for Organic Chemistry, Justus Liebig University Giessen and ended in january 2015. If you want to learn more about the project, please visit the SystemsX.ch website.

June 15th, Beilstein TV videos of AG Wegner online, watch here!

After their visit in March, the produced videos from Beilstein TV about the synthesis of a boron based bidentate Lewis acid catalyst developed in the Wegner group and the application of such a bidentate catalyst in organic synthesis are now online. The methodology and experiments are presented by Prof. Dr. Hermann A. Wegner, Luca Schweighauser and Sebastian Ahles.

 

Bidentate lewis acid catalysis for organic synthesis

 

Recipe for the preparation of a bidentate Lewis acid catalyst

 

May 07th, New Liebig-College Fellow

Wilfred "Jimmy" Marsh is the new Liebig-College fellow in the Wegner group.

The Wegner group would like to welcome Wilfred "Jimmy" Marsh as guest of the group. As a fellow of the Liebig-College scholarship, Jimmy Marsh from Nova-Scotia (Canada) will be working in the Wegner group until the end of august.

April 20th, New paper in JACS

Zhenpin Lu's paper about catalytic carbon dioxide reduction is now online available at JACS

We congratulate Zhenpin Lu that his paper "Aromaticity as Stabilizing Element in the Bidentate Activation for the Catalytic Reduction of Carbon Dioxide" was recently accepted by the Journal of American Chemical Society and is now as ASAP article available.

March 20th, Beilstein TV

Beilstein TV visited the Wegner group for the production of a video-clip about our research.

On March 17th & 18th, Beilstein TV was visiting the Wegner group, producing some short videos of specific synthesis procedures. The synthesis of the bidentate boron-based Lewis acid catalyst as well as Inverse Electron Demand Diels-Alder reactions catalysed by these bidentate Lewis acids were shown. We expect to be able to post the final video here in mid-april.

March 10th, New PhD Student

Marcel Strauss joined the Wegner group as a new research associate and PhD student.

New support for the Wegner group. Marcel Strauß joined the group as a new research associate and PhD student. He will be working on azo switches and boron based bidentate Lewis-acid catalysis.

January 20th, 2015, Goodbye Silvia

Silvia Bellotto obtained her doctoral degree after beginning her interdisciplinary PhD in December 2010.

The Wegner group would like to congratulate Silvia Bellotto to her doctoral degree. We hope you enjoyed your time in the Wegner group and wish you all the best for your future.

doc_hat_silviadoc_hat_silvia2doc_hat_silvia3