Distinct differences in the nanoscale behaviors of the twist–bend liquid crystal phase of a flexible linear trimer and homologous dimer

Abstract

We synthesized the liquid crystal dimer and trimer members of a series of flexible linear oligomers and characterized their microscopic and nanoscopic properties using resonant soft X-ray scattering and a number of other experimental techniques. On the microscopic scale, the twist–bend phases of the dimer and trimer appear essentially identical. However, while the liquid crystal dimer exhibits a temperature-dependent variation of its twist–bend helical pitch varying from 100 to 170 Å on heating, the trimer exhibits an essentially temperature-independent pitch of 66 Å, significantly shorter than those reported for other twist–bend forming materials in the literature. We attribute this to a specific combination of intrinsic conformational bend of the trimer molecules and a sterically favorable intercalation of the trimers over a commensurate fraction (two-thirds) of the molecular length. We develop a geometric model of the twist–bend phase for these materials with the molecules arranging into helical chain structures, and we fully determine their respective geometric parameters.

Uniform distortions and generalized elasticity of liquid crystals

“…This is indeed the only example of spontaneous chiral symmetry breaking known in a fluid in the absence of spatial order [25]. 11 Many experimental studies have claimed the existence of the N TB phase in a number nematogenic systems with various molecular motifs [26][27][28][29][30][31][32][33]. These studies agree in showing that the pitch of the modulated nematic structure, which indeed exhibits both chiralities, fall in the nanometric range.…”

“…For c 1 , c 2 , and d given by (26a), corresponding to the first family of uniform distortions obtained in Sec. II B, equation (32) reduces to the following three scalar linear equations,…”

Ether‐ and Thioether‐Linked Naphthalene‐Based Liquid‐Crystal Dimers: Influence of Chalcogen Linkage and Mesogenic‐Arm Symmetry on the Incidence and Stability of the Twist–Bend Nematic Phase

“…[16] Ramou et al reported that the N TB phase can be induced in mixtures of conventionaln ematic and nonmesogenic dimers. [17] Besides liquid-crystal dimers, the N TB phase has also been observedi nb ent-core molecules, [5,[18][19][20] oligomers, [21][22][23][24][25] and polymers. [3,4,26] Although the majority of twist-bend nematogens developeds of ar are achiral,t here have been af ew reports on formation of the N TB phase based on chiral bentshaped molecules,i nw hicht he chirality is located in the mesogenic-arm core, [27,28] terminal chain, [29] or spacer.…”

Twist-Bend Nematogenic Supramolecular Dimers and Trimers Formed by Hydrogen Bonding

“…By far the greatest number of twist-bend nematogens reported so far may be described as odd-membered liquid crystal dimers having a similar molecular curvature to CB7CB. However, the N TB phase has also been observed for rigid bent-core materials [24], a hybrid bent-core-calamitic dimer [25], trimers and tetramers [26][27][28][29], a hexamer [30], and main-chain polymers [31]. The common structural feature shared by all these molecular architectures is curvature, although this is not always uniform.…”