Designing banana-shaped liquid crystals without Schiff's base units: m-terphenyls, 2,6-diphenylpyridines and V-shaped tolane derivatives

Abstract

This paper reports attempts to obtain (anti)ferroelectric switchable achiral banana-shaped molecules without Schiff's base units. For this purpose we have synthesized novel V-shaped molecules consisting of rigid angular central units [1,3-disubstituted benzene, 2,7-disubstituted naphthalene, 1,3-diphenylbenzene, 2,6-diphenylnitrobenzene, 2,6-diphenylpyridine, 1,3-bis(phenylethynyl)benzene, 1-phenyl-3-(phenylethynyl)benzene] connected via ester linkages to two rigid cores (1,4-disubstituted benzenes, biphenyls, 2-phenylpyrimidines, phenylbenzoates). Most compounds have rather high melting points. Only molecules with seven aromatic rings show liquid crystalline properties. Two-dimensional modulated smectic phases (rectangular columnar phases) were found for molecules with phenylbenzoate rigid units. Intercalated fluid smectic phases were detected for the corresponding 2-phenylpyrimidine derivatives. For the first time in the case of banana-shaped molecules a nematic phase was observed for a 2′-nitro-m-terphenyl-4,4″-diyl bisbenzoate. However, none of the synthesized compounds exhibit the typical texture of the (anti)ferroelectric switchable mesophases, known from the Schiff's base derivatives.