A Twist‐Bend Nematic Phase Driven by Hydrogen Bonding

Abstract

The liquid crystalline phase behavior of 4-[6-(4'-cyanobiphenyl-4-yl)hexyloxy]benzoic acid (CB6OBA) and 4-[5-(4'-cyanobiphenyl-4-yloxy)pentyloxy]benzoic acid (CBO5OBA) is described. Both acids show an enantiotropic nematic phase attributed to the formation of supramolecular complexes by hydrogen bonding between the benzoic acid units. In addition, CB6OBA provides the first example of hydrogen bonding driving the formation of the twist-bend nematic phase. The observation of the twist-bend nematic phase for CB6OBA, but not CBO5OBA, is attributed to the more bent molecular shape of the complexes formed by the former, reinforcing the view that shape is a key factor in stabilizing this new phase. Temperature-dependent FTIR spectroscopy reveals differences in hydrogen bonding between the two nematic phases shown by CB6OBA which suggest that the open hydrogen-bonded complexes may play an important role in stabilizing the helical arrangement found in the twist-bend nematic phase.

Investigating the Cusp between the nano- and macro-sciences in supermolecular liquid-crystalline twist-bend nematogens

“…20,23,[39][40][41][42][43][44][45][46][47] Beyond simple dimers there exist examples of both covalent and non-covalent trimeric materials and one ''tetrameric'' material (T4 9 ) reported to exhibit this state of matter. [48][49][50][51] These materials are not strictly trimers or tetramers in that they are composed of identical sub units however they can be broken down into subdivisions which are broadly similar; for example the material T4 9 has four phenylbenzoate mesogenic units separated by three nonamethylene spacers and is therefore described as a tetramer.…”

Conformational landscapes of bimesogenic compounds and their implications for the formation of modulated nematic phases

“…A number of reviews concerning the twist-bend phase have been published recently [18][19][20]. A relatively large number of dimeric liquid crystals are known to exhibit this state of matter [1,3,8,9,11,12,[21][22][23][24][25][26][27][28][29][30], and there is a growing number of liquid-crystalline oligomers known to exhibit the twist-bend phase [18,[31][32][33][34]. Additionally, this phase has been observed in a phenylpiperazine derived bent-core liquid crystal [4].…”

Influence of internal flexibility on the double glass transition in a series of odd non-symmetric liquid crystal dimers characterised by dielectric measurements

“…Depending on the nature of the involved units we can distinguish between symmetric (both units are identical) and non-symmetric LC dimers with different rigid units in the molecule. The resulting material generally shows unusual properties as enhanced electro-optical properties and anysotropy, additional molecular motions, new mesophases (alternating and modulated smectic mesophases [2,3,[5][6][7][8][9], the recently discovered twist-bend nematic mesophase [10][11][12][13][14][15][16][17][18][19], . .…”