Novel discotic boroxines : synthesis and mesomorphic properties

Discotic liquid crystals have attracted the attention of many research groups worldwide. Due to the one dimensional charge and ion transport in the columnar mesophase, the ability of liquid crystals (LCs) to self-heal structural defects by thermal annealing and the ease of processing via spin coating, drop casting and other solution processing methods highly useful applications could be realized. Aryl boronic acids are valuable reagents for a number of metal-catalyzed reactions, and boroxines, the cyclic trimers of organoboronic acids, may serve as useful building blocks. However, surprisingly little is known about liquid crystalline boroxines. We described a new synthetic approach to highly substituted triphenylboroxines and investigated their liquid crystalline properties. The tris(3,4,5-trialkyloxy)phenyl functionalized derivatives showed broad mesophases for a minimum alkyl chain length of C9. Textures observed under polarizing optical microscope indicated a columnar hexagonal (Colh) mesophase geometry that was confirmed by X-ray diffraction experiments

A novel B,O,N-doped mesogen with narrowband MR-TADF emission

The St Andrews team would also like to thank EPSRC (EP/P010482/1, EP/W015137/1, EP/W007517/1) for financial support. E.Z.-C. was a Royal Society Leverhulme Trust Senior Research Fellow (SRF\R1\201089).Modification of an unsymmetric B,O,N-doped aromatic core with peripheral mesogenic units triggers self-assembly into a columnar hexagonal mesophase, which is stable between 22 and 144 °C. The columnar assembly is preserved in a glassy state below 22 °C. The B,O,N-doped mesogen displays narrowband sky-blue multiresonance thermally activated delayed fluorescence (MR-TADF) under diluted conditions and bright excimer emission in condensed phase. Our combined experimental and theoretical approach provides insight into the development of strongly aggregating liquid crystalline MR-TADF emitters.Peer reviewe

Das Zeitschriften-Paradoxon oder: Wer verfügt über wissenschaftliche Information?

Inhalt: Stephan, Werner: Begrüßung und Einführung - Graf, Bernhard: Zeitschriftenevaluation an der Universität Stuttgart. Ist die inhaltliche Bewertung ein hinreichendes Kriterium für Zeitschriftenabbestellungen? Ein Werkstattbericht - Kirchgässner, Adalbert: 13 Jahre Zeitschriftenabbestellungen an der Universität Konstanz. Die Auswirkungen der Preissteigerungen bei stagnierenden Etats auf das Zeitschriftenportfolio. Veränderungen des Nutzerverhaltens und Konsequenzen für die künftige Bestandspolitik (in einem einschichten System) - Laschat, Sabine: Braucht die Wissenschaft noch Zeitschriften? - Schüz, Wolfram: Das Zeitschriftenparadoxo

Intramolecular borylation via sequential B-Mes bond cleavage for the divergent synthesis of B,N,B-doped benzo[4]helicenes

Authors thank the Natural Sciences and Engineering Research Council of Canada and the Leverhulme Trust (RPG-2016-47) for financial support. J. A. Knöller thanks the Baden Württemberg Stiftung for a scholarship as well as Queen's and Stuttgart University for enabling this research through the Dual Degree Masters program.New symmetric and unsymmetric B,N,B-doped benzo[4]helicenes 3 - 6a/b have been achieved in good yields, using a three-step process, starting from N(tolyl)3 in a highly divergent manner (7 examples). A borinic acid functionalized 1,4-B,N- anthracene 1 was found to display unprecedented reactivity, acting as a convenient and highly effective precursor for selective formation of bromo substituted B,N,B-benzo[4]helicenes 2a/2b via intramolecular borylation and sequential B-Mes bond cleavage in presence of BBr3. Subsequent reaction of 2a/2b with Ar-Li provided a highly effective toolbox for the preparation of symmetrically/unsymmetrically functionalized B,N,B-helicenes. Their high photoluminescence quantum yields along with the small ∆EST suggest the potential as thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs).PostprintPeer reviewe

Intramolecular hetero-Diels-Alder reaction of prolinal-derived N-arylimines : Lewis acid-dependent reversal of the diastereoselectivity

Intramolecular Lewis acid-catalyzed hetero-Diels-Alder reaction of L-prolinal-derived N-arylimine 1 yielded diastereoselectively either the cis,cis-azacyclopenta[a]anthracene derivative 2a or the trans,trans-isomer 2b, depending on the Lewis acid

Diastereoselective synthesis of α-Hydroxy- and α-amino-indolizidines and -quinolizidines : evidence for a novel cyclization/hydride migration mechanism in the TiCl4-induced reaction of prolinalbenzylimines by deuterium labeling studies

Lewis acid-catalyzed cyclization of prolinal and 2-piperidine-carbaldehyde benzylimines 11, 12 results in the diastereoselective formation of α-amino-β-alkyl-substituted indolizidines 15, 17, 19, 21 and -quinolizidines 16, 18, 20, respectively. Both diastereoselectivity and constitution depend on the Lewis acid. FeCl3 yields α,β- trans-α-(benzylamino)-β-isopropenyl derivatives 15 and 16, probably by a cationic cyclization via carbenium ions 32a, b. In contrast, TiCl4 yields ,α,β- cis-α-(benzylideneamino)-β-isopropyl derivatives 19 and 20 by a novel cyclization/intermolecular hydride transfer mechanism, which was supported by deuterium labeling studies. Compounds 15, 16, 19, and 20 were converted to the diastereomeric acetamides 24, 25 and 28, 29. By an analogous cyclization of the aldehydes 8 and 9 only α ,β-cis-α-hydroxy--isopropenylindolizidines 51 and -quinolizidines 52 were obtained irrespective of the Lewis acid used. The structures of 30 and 52 were elucidated by X-ray analysis

Carbohydrates as chiral templates : stereoselective synthesis of (R)- and (S)-α-aminophosphonic acid derivatives

The stereoselective synthesis of diethyl (S)- or (R)-α-[(O-pivaloyl-hexapyranosyl) amino]benzylphosphonates is achieved via Lewis acid catalyzed addition of diethyl phosphite to O-pivaloylated N-benzylidene -β-D-galactosylamine or N-benzylidene-α-D-arabinopyranosylamine. The process can also be performed by a one-pot procedure selectively giving (S)-aminophosphonic acid derivatives from galactosylamine and (R)-aminophosphonic acid derivatives from β-L-fucosylamine as the chiral auxiliaries

Carbohydrates as chiral templates : stereoselective synthesis of (R)-homoallyl amines using L-fucose as the auxiliary formally enantiomeric to D-galactose

(R)-Homoallyl amines are synthesized with high asymmetric induction using the diastereoselective Lewis acid induced addition of allylsilanes and allylstannanes to Schiff bases of O-acyl protected fucopyranosylamine