| Summary: | A selection of novel non-symmetric supramolecular liquid crystal dimers and trimers formed by hydrogen-bonding have been prepared and their phase behaviour characterised by polarised optical microscopy, X-ray diffraction and temperature-dependent Fourier-transform infrared spectroscopy. We mix the bent twist-bend nematogen 4-[6-(4’-cyanobiphenyl-4-yl) hexyloxy]-benzoic acid (CB6OBA) with a series of small stilbazole-based compounds 4-[(E)-2-(n-alkoxyphenyl)ethenyl]pyridines (<i>n</i>OS) of varying terminal chain length (<i>n</i>) to obtain the CB6OBA:<i>n</i>OS complexes. Complexes with <i>n</i> ≤ 7 exhibit nematic and twist-bend nematic behaviour, followed on cooling by a smectic C phase for <i>n</i> = 4−7, and finally, a hexatic-type smectic X phase for <i>n</i> = 3−7. Mixtures with <i>n</i> = 8−10 exhibit a smectic A phase below the conventional nematic phase, and on further cooling, a biaxial smectic A<sub>b</sub> phase and the same hexatic-type SmX phase. Supramolecular trimers, CB6OBA:CB6OS and CB6OBA:1OB6OS, formed between CB6OBA and dimeric stilbazoles [(E)-2-(4-{[6-(4’-methoxy[1,1’-biphenyl]-4-yl)hexyl]oxy}phenyl)ethenyl]pyridine (1OB6OS) or 4-[(E)-4’-(6-{4-[(E)-2-(pyridin-4-yl)ethenyl]phenoxy}hexyl)[1,1’-biphenyl]-4- carbonitrile (CB6OS), exhibit nematic and twist-bend nematic phases, and are the first hydrogen-bonded trimers consisting of unlike donor and acceptor fragments to do so.
|
|---|
