Browsing by Author "Wöhrle, Tobias"

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Open Access
Columnar propeller‐like 1,3,5‐triphenylbenzenes : probing the effect of chlorine on the Suzuki cross‐coupling and liquid crystalline properties
(2020) Grunwald, Marco André; Wöhrle, Tobias; Forschner, Robert; Baro, Angelika; Laschat, Sabine
Suzuki cross‐couplings either between chlorinated N‐methyliminodiacetic acid (MIDA)‐protected aryl boronates and 1,3,5‐tribromobenzene or between chlorinated aryl bromides and phenyltrisboronic species to star‐shaped 1,3,5‐triphenylbenzenes with different substitution patterns and chloro substituents at the outer phenyl rings were studied. The chlorinated precursors required for the respective reaction were synthesized and characterized. Depending on the used coupling reaction target triphenylbenzenes were isolated in yields between 42 % and 88 %. Their mesomorphic properties were influenced by the substitution pattern and number of peripheral chlorine atoms. Triphenylbenzene with 3,5‐alkoxy substitution and H in para‐position self‐assembled into either columnar hexagonal (Colh) mesophases or a soft crystal. While threefold chloro substitution in meta‐position of the outer phenyl rings led to stable room temperature Colho phases, triphenylbenzenes with threefold para‐chloro or 3,5‐dichloro substitution were non‐mesomorphic. Based on X‐ray diffraction data a helical packing model for the observed phases similar to that of related alkoxy‐substituted triphenylbenzenes was proposed.
Open Access
Novel discotic boroxines : synthesis and mesomorphic properties
(2014) Wöhrle, Tobias; Baro, Angelika; Laschat, Sabine
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.