Electro-optical properties of the nematic phase in V-shaped molecules with a 2,3-naphthalene central unit

Abstract

So far there is little understanding of the physicochemical properties of the nematic phase of V-shaped bent-core liquid crystalline (VBLC) molecules. We have synthesized VBLC molecules based on a 2,3naphthalene central unit, varying the carbon number of the flexible alkyl chains (n ¼ 2, 6 or 12) to extend the nematic range. We examined the polar and biaxial properties of the nematic phases for two homologous molecules with n ¼ 6 and 12.

Mesogens with central naphthalene core substituted at various positions

“…Such materials are referred to acute angle mesogens, U-shaped, and/or V-shaped liquid crystals, respectively. The 1,2-disubstituted naphthalene-derived bent-shaped materials exhibited conventional SmA phases and the same was for naphthalene-2,3-diol derivatives, where SmA phase [23,24,28] and N-SmA phase sequence [27,29,30] were identified, suggesting that molecules in this phases are free to rotate around the axis of symmetry. More interesting results have been reported in the series of naphthalene-1,7-diol derivatives: the crystalline B 4 phase was identified in the PIMB-derivatives with a terminal alkoxy tail [24,34,37].…”

“…The previously reported naphthalenediol-based 2,3-disubstituted materials exhibited a nematic and SmA phase [23,28,30]; however, the material VIIc was crystalline only. Finally, introduction of the side arms to position 1,7 of the naphthalene ring resulted, both in the naphthalenediol-based compounds [23,26] and in the studied compound of IXc, in the loss of mesomorphic properties or formation of higher organised phases.…”

“…On the other hand, joining the lengthening arms to the naphthalene-1,2-diol [23,24], naphthalene-2,3diol [23,24,[27][28][29][30] and naphthalene-1,7-diol [23,24,[31][32][33][34][35][36][37][38][39][40], and to 1,2-positions of benzene [41][42][43][44][45], results in bending angle around 60°. Such materials are referred to acute angle mesogens, U-shaped, and/or V-shaped liquid crystals, respectively.…”

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.…”