Molecular shape as a means to control the incidence of the nanostructured twist bend phase

Abstract

Liquid crystalline phases with a spontaneous twist-bend modulation are most commonly observed for dimers and bimesogens with nonamethylene spacers. In order to redress this balance we devised a simple chemical intermediate that can be used to prepare unsymmetrical bimesogens; as a proof of concept we prepared and studied eleven novel materials with all found to exhibit the twist-bend phase and exhibit a linear relationship between TN-I and TTB-N. A computational study of the conformational landscape reveals the octamethyleneoxy spacer to have a broader distribution of bend-angles than the nonamethylene equivalent, leading to reductions in the thermal stability of the TB phase. This result indicates that a tight distribution of bend-angles should stabilise the TB phase and lead to direct TB-Iso phase transitions, and conversely a broader distribution should destabilise the TB phase which may allow new states of matter that are occluded by the incidence of this phase to be revealed.

A Novel Nematic-Like Mesophase Induced in Dimers, Trimers and Tetramers Doped with a Highly Chiral Additive

“…16 This phase is principally exhibited by liquid-crystalline dimers, 17 in which two rigid sections are adjoined by a (semi) flexible spacer. Experimental results suggest it is primarily molecular shape [18][19][20] and the gross bend-angle that appear to dictate the incidence of this phase, [20][21][22] supporting the findings of earlier theoretical treatments. 23,24 In addition to low molecular weight dimers the TB phase is also found in oligomers, [25][26][27][28] polymers 29,30 and possibly lyotropic systems.…”

Molecular Flexibility and Bend in Semi‐Rigid Liquid Crystals: Implications for the Heliconical Nematic Ground State

“…The twist-bend modulated nematicp hase (TB), the averageo rientation of the nematic phase rotateso ver af ew nanometers giving ah elical structure with ar emarkably short pitch length. [20] Experimental resultss uggest it is primarily molecular shape [14,21,22] and the gross bend-angle whicha ppeart odictatet he incidenceo ft his phase, [14,23,24] supporting the findings of earliert heoretical treatments. [10][11][12] Although this phase is principally exhibited by liquid-crystalline dimers, in which two rigid sections are adjoined by a( semi-) flexible spacer, [13,14] it has also been observed in semi-rigid bent-core materials, [15] liquid crystalline nmers [16][17][18][19] and polymers.…”

Pentaerythritol Derived Tetrapode Exhibiting a Nematic‐Like Mesophase at Ambient Temperatures

“…Using the procedure outlined by Archbold et al., we generated a library of conformers for 1 using the AM1 semi‐empirical method, before calculating the probability of a given bend angle between two opposing mesogenic units as shown in Figure c. The probability weighted bend‐angle is 98°, however the distribution of bend angles is rather broad due to the sheer number of conformers – we find the FWHM of a Gaussian fit to the major peak (Figure c) to be 45°, far larger than that of simple LC dimers such as CB9CB (19 °C) and CB8OCB (31 °C) . There is also a significant population of hairpin conformers, defined here as those with a bend‐angle of less than 60°.…”

“…The probability weighted bend-angle is 98°, however the distribution of bend angles is rather broad due to the sheer number of conformers -we find the FWHM of a Gaussian fit to the major peak (Figure 3c) to be 45°, far larger than that of simple LC dimers such as CB9CB (19°C) and CB8OCB (31°C). [8] There is also a significant population of hairpin conformers, defined here as those with a bend-angle of less than 60°. The flexibility of the material and large number of conformers it can adopt probably contribute significantly to the absence of a crystalline solid (the material forms a glass on cooling) and low clearing point.…”