Tuning the mesogenic properties of 5-alkoxy-2-(4-alkoxyphenyl)pyrimidine liquid crystals: the effect of a phenoxy end-group in two sterically equivalent series

Abstract

Lemieux (2014) Tuning the mesogenic properties of 5-alkoxy-2-(4-alkoxyphenyl)pyrimidine liquid crystals: the effect of a phenoxy end-group in two sterically equivalent series, Liquid Crystals, 41:9, 1246-1260, Two sterically equivalent series of phenoxy-terminated 5-alkoxy-2-(4-alkoxyphenyl)pyrimidine liquid crystals were synthesised, and their mesogenic properties were characterised by polarised optical microscopy and differential scanning calorimetry (DSC). The phenoxy end-group causes a significant increase in melting point and inhibits -at least partially -the mesomorphism of these materials relative to the parent isomers; in most cases, the broad enantiotropic SmC phase formed by the parent isomers is suppressed by the addition of the phenoxy endgroup. However, detailed analyses by small-angle X-ray scattering and monodomain 2D X-ray scattering suggest that these compounds form a SmA phase with a partially intercalated bilayer structure in which the phenoxy endgroups are nanosegregated. Such an intercalated bilayer structure might enable the tuning of smectogenic properties by appropriate substitution of the phenoxy end-groups.

Shape segregation in molecular organisation: a combined X-ray scattering and molecular dynamics study of smectic liquid crystals

“…Phenoxy end-groups have been reported to suppress SmC phases, 19 and the positions of fluorine substituents on phenoxy end-groups have been shown to influence the relative stabilities of the SmA and SmC phases. 20 In some cases, bulky non-polar end-groups have been proposed to preclude liquid-crystalline phases 16 and weaken interlayer interactions 21 due to their volume, but other studies have suggested that such groups may increase the temperature range over which the SmA phase is stable, 18 or enhance the stability of the SmC phase over the SmA phase.…”

Tuning the mesomorphic properties of phenoxy-terminated smectic liquid crystals: the effect of fluoro substitution

“…28 In the monofluoro series QL20-m/n-xF, we chose to examine the same three representative isomers featured in Fig. 18 As shown in Fig. Modeling of intermolecular correlations in the SmA phase formed by the parent isomers QL11-m/n suggest that the phenylpyrimidine cores are approximately in register in the intercalated bilayer structure formed by QL11-10/6, and partially offset to bring the pyrimidine rings in register in the case of QL11-8/8, and the phenyl rings in register in the case of QL11-12/4.…”

“…18 To assess the validity of these measurements, the samples were doped with the chiral additive MDW797 (2-5 mol%) and tilt angles were measured electrooptically by switching the SmC* phase between opposite tilt orientations as SSFLC films aligned in the same glass cells. 18 To assess the validity of these measurements, the samples were doped with the chiral additive MDW797 (2-5 mol%) and tilt angles were measured electrooptically by switching the SmC* phase between opposite tilt orientations as SSFLC films aligned in the same glass cells.…”

“…7,15 The design features of these materials include a trisiloxane or tricarbosilane end-group together with a SmA-promoting element such as a chloroterminated alkyl chain or a 5-phenylpyrimidine core. 17 In the process of developing a diverse library of 'de Vries-like' mesogens, we have sought to expand the scope of nanosegregating elements in a new design that includes phenoxy end-groups, 18 which should segregate from alkyl chains at the smectic layer interface by virtue of their strong non-covalent interactions, and perhaps enable the tuning of mesomorphic properties by appropriate aromatic substitution. 17 In the process of developing a diverse library of 'de Vries-like' mesogens, we have sought to expand the scope of nanosegregating elements in a new design that includes phenoxy end-groups, 18 which should segregate from alkyl chains at the smectic layer interface by virtue of their strong non-covalent interactions, and perhaps enable the tuning of mesomorphic properties by appropriate aromatic substitution.…”

“…19 There are few reports of arene-terminated mesogens in the literature, which are mostly limited to homologous series of nematogens that exhibit pronounced odd-even effects in their N-I transition temperatures. 18 A comparison of the mesomorphic properties of QL11-m/n with those of the parent isomers lacking the end-group (2PhP-m/n) showed that the phenoxy end-group causes a significant increase in melting point and reduces the mesomorphic range of these materials. 18 A comparison of the mesomorphic properties of QL11-m/n with those of the parent isomers lacking the end-group (2PhP-m/n) showed that the phenoxy end-group causes a significant increase in melting point and reduces the mesomorphic range of these materials.…”