Origin of Self-Assembled Helical Supramolecular Structures in Achiral C6 Biphenyl Carboxylic Acid Compounds

Abstract

To understand the formation mechanism of helical supramolecular structures in the smectic C (SmC) liquid crystalline (LC) phase of BPCA-Cn-PmOH (n is the number of methylene units, n ) 6-10

Mirror symmetry breaking in liquids and liquid crystals

“…Chiral domains were also observed in SmC phases of simple rod-like molecules [101][102][103][104], lacking any polar packing. In this case surface induced chiral modes of director alignment appear to be mainly responsible for the observed effects [36,85,105].…”

“…The discovery of chirality and spontaneous symmetry breaking in the polar smectic phases of bent-core LCs had a huge impact and stimulated intensive research, leading to further examples of spontaneous mirror symmetry breaking in other LC phases of bent-core molecules [94][95][96], as well as in LC phases of other achiral molecules, including rod-like, polycatenar and disc-like, thus leading to chirality in columnar [97], cubic [98,99], low temperature smectic [100], tilted smectic [94,96,[101][102][103][104][105] and nematic phases [94,[106][107][108][109][110], in the ground state or under the influence of external electric fields [111][112][113].…”

Structures and phase transformations of odd-numbered asymmetric main-chain liquid crystalline polyesters

“…For the high-temperature transition, the heat of transition and the onset transition temperature at the high-temperature side do not exhibit cooling rate dependence. This indicates that the high-temperature transition takes place close to thermodynamic equilibrium, and it may be associated with the transitions between an isotropic melt (I) and a low ordered LC phase [28][29][30][31][32][33][34][35]. In contrast, the heat of transition (6.5 kJ/mol) at the lower transition temperature and its onset transition temperature are cooling rate dependent, which is often observed during polymer crystallization processes.…”

“…In the odd-numbered BPE-Cn, there is neither the helical supra-molecular texture (which exists in BPCA-Cn-PmOH, its monomer) [28,29], nor the ring striation with three different colors (which are observed in the corresponding evennumbered BPE-Cn) [30]. This is because that the oddnumbered BPE-Cn have neither a large zigzag conformation in their polymer chains nor a continuous twisting of the chemical repeat unit from one to another along the same twisting direction.…”

“…We recently reported that a three-dimensional (3D) helical supramolecular structure formed in a synclinically tilted smectic C (SmC S ) phase of the achiral a,u-carboxylic acidhydroxyl terminated series of compounds with different methylene spacer units (BPCA-Cn-PmOH, nZ6-10) [28,29]. When this series of A-B type asymmetric BPCA-Cn-PmOH compounds was polymerized, the corresponding polyesters (BPE-Cn) having a bend due to the meta-linkage in its chemical structure were obtained.…”