Novel Columnar Tetraphenylethenes via McMurry Coupling

Several tetraphenylethenes 2a, 4a–i with lipophilic side chains were synthesized and their mesomorphic properties were investigated. The most promising candidates turned out to be tetrakis[4‐(trisalkyloxybenzoyloxy)phenyl]ethenes 4e–i with chain lengths between C7 and C12. Compounds 4 were prepared by a convergent strategy employing a McMurry coupling of 4,4′‐dimethoxybenzophenone 1c, followed by demethylation and subsequent esterification of 2c with either 4‐decyloxybenzoic acid 3a, 3,4‐didecyloxybenzoic acid 3b, or O‐alkylated gallic acids 3c–i. Despite the twisting of the central tetraphenylethene moiety compounds 4c–i display hexagonal columnar mesophases according to differential scanning calorimetry (DSC), polarizing microscopy, and X‐ray diffraction studies. Even molecules devoid of a flat core region are able to form columnar mesophases. Here the viability of developing tetraphenylethenes displaying liquid crystallinity is examined. It is revealed that, despite the propeller shape of the tetraphenylethene core, peripheral gallic acid groups provide sufficient stabilization for hexagonal columnar mesophases to form (see Figure for possible arrangement).