The SmA phase of a bent-core V-shaped compound: structure and electric-field response

Abstract

2010) The SmA phase of a bent-core V-shaped compound: structure and electric-field response,The smectic A (SmA) phase of a V-shaped mesogen with a molecular bending angle of 60 • was studied. According to X-ray measurements, the molecules are arranged with the 'bow-string' direction parallel to the smectic layer. This point was confirmed by birefringence analysis and the result is compatible with a non-polar structure. A detailed study of the (001) smectic layer reflection versus temperature was also carried out to determine the smectic translational order parameter. The results indicate that the material presents a high degree of translational order. In addition, the electric field response of the material was studied by means of second harmonic generation. This technique turned out to be highly sensitive to small structural distortions due to the V-shape of the constituent molecules.

Smectic A–hexagonal columnar–B7 phase transition of acute-angle bent-core molecules

“…Differential scanning calorimetry (DSC) thermograms, along with transition temperatures and associated enthalpies, are shown in Fig. 1 and Table 1 for N(1,7)-EIE-Sn (n ¼ 16,18,20). At a glance, all thermograms similarly displayed isotropisation points over 250 C and three exothermic peaks upon cooling.…”

“…One controversial example is related to acute-angle bent-core molecules comprising a 2,3-naphthalene core with ester-type side wings. These molecules have been reported as switchable by Choi et al 17,18 but non-switchable by Ros et al 19,20 in the smectic phase. Thus, we believe a species of acute-angle bent-core mesogens can be an ultimate example that lies on the line between the banana-like and calamitic LC properties.…”

“…14,16 Their mesomorphic properties as a result of extension of the mesogenic part, including their molecular accommodation within the LC phase, were investigated. The V-shaped mesogens are designated as N(1,7)-EIE-Sn (n ¼ 16,18,20), where n denotes the number of carbon atoms in the terminal alkylthio tails.…”

Synthesis and structure of lateral halogenated V-shaped liquid crystal molecules based on a 1,7-naphthalene central core and alkylthio tails

“…[8][9][10] Matsuzaki et al [11,12] were the first to synthesise V-shaped molecules of about 60°based on 1,2-phenylene and 2,3-naphthalene central core, which only show conventional SmA and Nematic phase. Choi [13,14] and Ros et al [15] have also reported some V-shaped molecules based on the 2,3-naphthalene central unit with ester type side wings, but no B phase appears for these acute-angle liquid crystal materials. In general, the introduction of obtuse angle bent-core had been thought to be essential to form the previously mentioned switchable B phases.…”

Determination of the n-director direction of low bend-angle banana-shaped molecules by solid-state 13C NMR

“…Consequently, it remains controversial whether the molecular arrangements in the mesophases of these compounds are banana-like or calamitic, as discussed by Choi et al 16,17 and Ros et al 18,19 with different interpretations. Both prepared homologous series based on 2,3-naphthalene central cores; Choi et al claimed a polar SmA phase whereas Ros et al reported a nonpolar SmA.…”