Mirror Symmetry Breaking and Network Formation in Achiral Polycatenars with Thioether Tail

Abstract

Mirror symmetry breaking in systems composed of achiral molecules is of importance for the design of functional materials for technological applications as well as for the understanding of the mechanisms of spontaneous emergence of chirality. Herein, we report the design and molecular selfassembly of two series of rod-like achiral polycatenar molecules derived from a π-conjugated 5,5'-diphenyl-2,2'bithiophene core with a fork-like triple alkoxylated end and a variable single alkylthio chain at the other end. In both series of liquid crystalline materials, differing in the chain length at the trialkoxylated end, helical self-assembly of the π-con-* ] ). Further chain elongation results in removing the I23 phase and the re-appearance of the Ia � 3d phase with different pitch lengths. In the second series an additional tetragonal phase separates the two cubic phase types.

Alkylthio-based asymmetric liquid crystals: unravelling the substituent effects and intercalated cybotactic nematic and smectic phases

“…Among the homologs bearing longer alkyl chains, the SmC phase was observed in OO7 42,45,46 and SO8, but not in SS8, 34 thereby indicating that the alkylthio group hindered the formation of an Sm phase in SSn. The alkylthio group can either induce the formation of a highly ordered phase due to the enhanced intermolecular interactions, 4,27,40 or hinder the Sm phase formation through the greater conformational and steric effects. 30,34 These trends are counterbalanced by the anisotropy of the mesogenic core structures and the alkyl chains.…”

“…These properties arise from the longer C-S bond lengths (B1.7 Å) and the smaller C-S-C bond angles (B1001) than those of alkyl and alkoxy groups (e.g., B1.5 and B1.4 Å for the C-C and C-O bond lengths; and B1101 and 1181 for the C-CH 2 -C and C-O-C bond angles, respectively). Such steric effects of the alkylthio groups have benefits in inducing not only the above-mentioned Col phase, 22,23 but also the cubic phase, 27 which could effectively fill large spaces around the columns and gyroids in terms of free volume effects. 28 In contrast, the greater flexibility and steric bulkiness imparted by the C-S-C bonds prevent rod-like molecules from rearranging into LC phases and reduce the LC temperature ranges.…”

Transition from lamellar to nanostructure mesophases in azobenzene-based hockey-stick polycatenars

“…Cub [ * ] with I23 symmetry (Cub [ * ] /I23) as would be expected upon alkyl-chain elongation. 14,15,28 However, the type of the Cub bi does not change with increasing the length of the terminal chains, indicating that the required chain volume is not achieved.…”

“…5,[7][8][9] Therefore, the design and synthesis of new functional cubic LCs are essentials for the development of current and future applications of LCs. Cub bi phases are common for non-symmetric polycatenar LCs [10][11][12][13][14][15] but rare for bent-core LCs (BCLCs). [16][17][18][19] Polycatenars are rod-like molecules terminated with more than two flexible chains.…”

“…23 Moreover, mirror symmetry breaking was also observed in the isotropic liquid phase assigned as Iso phase in non-symmetric polycatenars. [10][11][12][13][14][15]24 Using alkyl chain engineering, we were able to report different types of functional nanostructured azobenzene-based non-symmetric polycatenars exhibiting Iso 1 [ * ] phase beside a lamellar (Smectic A = SmA) phase in tricatenar systems 25,26 or Cub bi or 3D tetragonal phases in tetracatenar molecules. 12,21,23,24,27,28 An efficient way to photocontrol the molecular structure and to improve the physical properties toward applications such as optoelectronic sensing devices 29 and organic light-driven actuators [30][31][32] is the incorporation of the azobenzene unit into the molecular structure.…”