Mesomorphic properties of cyanobiphenyl dimers with a substituted central malonate unit: overruling effect of fluorination. Issue 10 (9th August 2022)

• Record Type: Journal Article
• Authors: Grunwald, Marco André; Egler-Kemmerer, Alexander-Nicholas; Bauch, Soeren Magnus; Ebert, Max; Bräuning, Gabriele; Zens, Anna; Laschat, Sabine
• Is Part Of: Liquid crystals. Volume 49:Issue 10(2022)
• Page Start: 1347
• Page End: 1358
• Publication Date: 2022-08-09
• Subjects: Cyanobiphenyl -- dimer -- malonate -- perfluorinated -- nanosegregation -- packing model -- substitution; Liquid crystals -- Periodicals; 548.905
• DOI: 10.1080/02678292.2022.2031327
• Languages: English
• ISSNs: 0267-8292

Abstract

ABSTRACT: Two series of C2-substituted dimers carrying a central C2-hexyl- or C2-nonafluorohexyl malonate and two cyanobiphenyls attached via alkoxy spacers of various lengths (n = 6–12) were synthesised, and the mesomorphic properties were studied by differential scanning calorimetry, polarising optical microscopyand X-ray diffraction (wide-angle and small-angle X-ray scattering). The C2-substituent dimers together with the spacer lengths had a pronounced influence on the phase behaviour. In case of C2-hexyl-substituted dimers, shorter spacers favoured N phases (n = 6–9), while longer spacers favoured SmA phases (n ≥ 9). In addition, decreased clearing temperatures were observed. In contrast, C2-nonafluorohexyl-substituted dimers suppressed N phases and displayed only SmA phases. Moreover, clearing temperatures and phase stabilities considerably increased. Based on the experimentally determined layer thickness, a packing model for the SmA phases was proposed, where C2-substituted dimers displaced mesophases with molecules in a Y-conformation. As a result, less stable mesophases for C2-hexyl-substituted dimers due to weakened intermolecular interactions and more stable mesophases for C2-nonafluorohexyl-substituted dimers due to the fluorophobic effect and nanosegregation were obtained. Graphical Abstract: uf0001