Publications by authors named "Matthias Bremer"

11 Publications

  • Page 1 of 1

Vibrational circular dichroism studies of exceptionally strong chirality inducers in liquid crystals.

Phys Chem Chem Phys 2021 Apr;23(16):10021-10028

Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.

7,7'-Disubstituted 2,2'-methylenedioxy-1,1'-binaphthyls are highly efficient chirality inducers in nematic liquid crystals. The absolute configuration of these compounds is, however, hard to determine as they only crystallize as racemic mixtures. In this work a Vibrational Circular Dichroism (VCD) study is reported that provides an unambiguous determination of the absolute configuration of these compounds. An in-depth General Coupled Oscillator (GCO) analysis of the source of the VCD signal reveals that the unusual structure of these binaphthyl compounds inherently leads to strong and robust VCD bands. Combined with linear transit calculations, our VCD studies allow for the determination of key structural parameters.
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http://dx.doi.org/10.1039/d1cp00854dDOI Listing
April 2021

Synthesis of organic liquid crystals containing selectively fluorinated cyclopropanes.

Beilstein J Org Chem 2020 14;16:674-680. Epub 2020 Apr 14.

School of Chemistry, Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, United Kingdom.

This paper describes the synthesis of a series of organic liquid crystals (LCs) containing selectively fluorinated cyclopropanes at their termini. The syntheses used difluorocarbene additions to olefin precursors, an approach which proved straightforward such that these liquid crystal candidates could be efficiently prepared. Their physical and thermodynamic properties were evaluated and depending on individual structures, they either displayed positive or negative dielectric anisotropy. The study gives some guidance into effective structure-property relationships for the design of LCs containing selectively fluorinated cyclopropane motifs.
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http://dx.doi.org/10.3762/bjoc.16.65DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7176930PMC
April 2020

Inverted Carbon Geometries: Challenges to Experiment and Theory.

J Org Chem 2015 Jun 5;80(12):6520-4. Epub 2015 Jun 5.

§Institute of Organic Chemistry, Justus-Liebig University, Heinrich-Buff-Ring 58, 35392 Giessen, Gemany.

Disproving a long C-C-bond textbook example: The reported 1.643 Å C-C bond in 5-cyano-1,3-dehydroadamantane was redetermined and "only" amounts to 1.584 Å. While this value is well reproduced with ab initio methods, some common DFT approaches perform poorly and are only consistent with CCSD(T)/cc-pVTZ optimizations for noninverted carbons. Large deviations from experiment were also found for other molecules with atypical electron density distributions, e.g., cubane, bicyclo[2.2.0]hexane, and bicyclo[2.1.0]- and bicyclo[1.1.1]pentane, thereby presenting challenging structures for some DFT implementations.
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http://dx.doi.org/10.1021/acs.joc.5b00845DOI Listing
June 2015

Hypervalent sulfur fluorides and the design of liquid crystals.

Chimia (Aarau) 2014 ;68(6):363-70

Merck KGaA, Liquid Crystals R&D Chemistry Frankfurter Str. 250, 64293 Darmstadt, Germany.

Hypervalent sulfur fluorides are providing functional materials - such as liquid crystals - with unique physicochemical properties and new geometric structural elements.
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http://dx.doi.org/10.2533/chimia.2014.363DOI Listing
September 2014

The TV in your pocket: development of liquid-crystal materials for the new millennium.

Angew Chem Int Ed Engl 2013 Aug;52(34):8880-96

Merck KGaA, Liquid Crystal R&D, Frankfurter Strasse 250, 64293 Darmstadt, Germany.

New liquid crystals with very low viscosity, good mesophase behavior, and high reliability are necessary to achieve the breakthrough from flat computer monitors to large displays for television. Fluorine plays a decisive role not only because of the polarity it induces in organic molecules but also because of its low polarizability and weak propensity for ion solvation. In addition, subtle stereoelectronic effects in fluorine-containing liquid crystals influence material properties and allow these to be tuned to some extent to achieve the desired outcome. Some fairly sophisticated chemistry is required that is normally ruled out in the specialty chemicals industry because of cost. The television display market is now entering a phase of saturation. The broad availability of the internet has led to an ever increasing tendency for mobile products. Tablet PCs and smartphones require touch-panel functionality and low power consumption. New LCD modes with high-performance liquid crystals and additional components, such as polymerizable materials, can be used in such products.
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http://dx.doi.org/10.1002/anie.201300903DOI Listing
August 2013

Extraction of guided modes from organic emission layers by compound binary gratings.

Opt Lett 2012 Jul;37(13):2646-8

Institute of Electrical and Information Engineering, Christian-Albrechts-Universität zu Kiel, Kaiserstr. 2 24143 Kiel, Germany.

The extraction of guided modes from a 100 nm organic emission layer by compound binary gratings with multiple superimposed periods at different ratios is investigated. We measure angle-dependent photoluminescence from samples with double-period (350 and 450 nm), triple-period (350, 400, and 450 nm), and multiperiod (350, 400, 450, and 500 nm) gratings and show that each period component produces two outcoupling features due to first-order Bragg scattering of the TE(0) guided mode. The averaged angular color change is reduced by up to a factor of 11 compared to a single-period grating structuring.
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http://dx.doi.org/10.1364/OL.37.002646DOI Listing
July 2012

Understanding fluorine effects in liquid crystals.

Chemphyschem 2010 Feb;11(2):357-60

New Technology Office, Merck Ltd. Japan, 4084 Nakatsu, Aikawa-machi, Aiko-gun, Kanagawa 243-0303, Japan.

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http://dx.doi.org/10.1002/cphc.200900745DOI Listing
February 2010

Liquid crystals carrying stereodefined vicinal difluoro- and trifluoro- alkyl motifs.

Chem Commun (Camb) 2007 Dec 3(47):5075-7. Epub 2007 Oct 3.

School of Chemistry and Centre for Biomolecular Sciences, University of St Andrews, North Haugh, St Andrews, Fife, UK KY16 9ST.

The synthesis of the stereospecifically fluorinated difluoro- and trifluoro- rac-3 and rac-4 is described where the fluorine atoms are positioned adjacent/vicinal to each other and the physical characteristics of these candidate liquid crystals including negative dielectric anisotropy are measured and rationalised.
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http://dx.doi.org/10.1039/b711839bDOI Listing
December 2007

Difluorooxymethylene-Bridged Liquid Crystals: A Novel Synthesis Based on the Oxidative Alkoxydifluorodesulfuration of Dithianylium Salts.

Angew Chem Int Ed Engl 2001 Apr;40(8):1480-1484

Merck KGaA, Liquid Crystals Division 64271 Darmstadt (Germany) Fax: (+49) 6151-72-2593.

Insertion of a difluorooxymethylene bridge into the mesogenic core structure of phenylcyclohexane-based liquid crystals results in a class of materials that exhibits a surprising and unprecedented improvement of essentially all application-relevant properties. A novel synthetic procedure allows the convenient large-scale preparation of a variety of compounds based on α,α-difluoroalkyl ether structures.
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http://dx.doi.org/10.1002/1521-3773(20010417)40:8<1480::AID-ANIE1480>3.0.CO;2-MDOI Listing
April 2001

Nematic Liquid Crystals for Active Matrix Displays: Molecular Design and Synthesis.

Angew Chem Int Ed Engl 2000 Dec;39(23):4216-4235

Merck KGaA, Liquid Crystals Division 64271 Darmstadt, Germany, Fax: (+49) 6151-722593.

Substances forming calamitic mesophases have been known for more than 100 years but only the recent, rapid advance in active matrix liquid crystal display (AM-LCD) technology helped these materials to achieve the crucial position in flat panel display technology they hold today. Due to their high contrast, large viewing angle, and rapid switching times, modern AM-LCDs offer a superior picture quality even compared to conventional cathode ray tubes. Their flatness, low weight, and low energy consumption render them the technology of choice for all kinds of portable devices. Some of the future promises of AM-LCD technology are centered around the development of liquid crystalline materials for the different subtypes of active matrix applications. This development is aimed, on the one hand, towards improved electrooptical and viscoelastic properties; on the other hand, the increasing performance of LCDs leads to extremely stringent reliability demands on the liquid crystals. Responding to these high standards of performance and quality, most liquid crystals for contemporary AM-LCD applications are multiply fluorinated compounds with very high purities, as is typical for materials used in the electronics industry. The synthesis of these superfluorinated materials (SFMs) often requires specialized methods, which, in several cases, had to be introduced for the first time into the canon of industrial production. The immense market pressure, as well as the rapid advance of AM-LCD technology on the side of the display manufacturers, urges an increasing pace of the materials development. This demand for new materials can no longer be fulfilled by conventional trial-and-error approaches. As in the pharmaceutical industry, in the search for new, superior liquid crystals, the purely empirical methods are increasingly supported by a rational design based on computational methods.
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http://dx.doi.org/10.1002/1521-3773(20001201)39:23<4216::AID-ANIE4216>3.0.CO;2-KDOI Listing
December 2000