New phase sequences in banana-shaped mesogens: influence of fluorine substituent in compounds derived from 2,7-dihydroxynaphthalene

Abstract

The synthesis and characterization of several new banana-shaped mesogens derived from 2,7-dihydroxynaphthalene are described. Some new phase sequences such as N A

A polar biaxial smectic A phase in new unsymmetrical compounds composed of bent-core molecules

“…A DSC thermogram obtained for compound 12 is shown in figure 1. Although the clearing enthalpy is quite high, that of the mesophase-mesophase transition is rather small, about 0.1 kJ mol 21 .…”

“…All the compounds exhibiting the polar biaxial SmA phase studied by us so far [19][20][21] have been derived from 3-hydroxybenzoic acid. In order to explore other possibilities, we have investigated a few compounds derived from resorcinol but substituted unsymmetrically.…”

“…We earlier reported [20] another homologous series compounds 1g, many of which showed two types of mesophase, which were characterized as uniaxial smectic A phase with a partial bilayer structure (SmA d ), and a partial bilayer biaxial smectic A (SmA db ) phase. This SmA db phase has now been established as a polar phase with antiferroelectric characteristics [21,28] and has been designated as SmA d P A . These two series of compounds are isomeric, having the positions of the terminal cyano and the n-alkoxy chains interchanged.…”

“…Many of these exhibit the biaxial SmA phase. Very recently [21] we have shown that the biaxial smectic A phase reported earlier [19,20] is actually a polar partially bilayer biaxial smectic A (SmA d P A ) phase. It would not be out of place to mention here that Prehm et al [22] have observed a biaxial SmA phase in some rod-like bolaamphiphiles containing a long semiflourinated chain.…”

“…31, NO. 4, APRIL 2004, 567-578 The design and synthesis of unsymmetrical compounds exhibiting mesophases have not been explored thoroughly, particularly in compounds containing only one terminal chain and a small substituent at the other end [19][20][21]25]. In this paper, we report the synthesis and characterization of several unsymmetrical compounds, which are derived from 3-hydroxybenzoic acid as well as 1,3-dihydroxybenzene.…”