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

This paper reports attempts to obtain (anti)ferroelectric switchable achira l banana-shaped molecules without Schiff's base units. For this purpose we have synthesized novel V-shaped molecules consisting of rigid angular centr al units [1,3-disubstituted benzene, 2,7-disubstituted naphthalene, 1,3-dip henylbenzene, 2,6-diphenylnitrobenzene, 2,6-diphenylpyridine, 1,3-bis(pheny lethynyl)benzene, 1-phenyl-3-(phenylethynyl)benzene] connected via ester li nkages to two rigid cores (1,4-disubstituted benzenes, biphenyls, 2-phenylp yrimidines, phenylbenzoates). Most compounds have rather high melting point s. Only molecules with seven aromatic rings show liquid crystalline propert ies. Two-dimensional modulated smectic phases (rectangular columnar phases) were found for molecules with phenylbenzoate rigid units. Intercalated flu id smectic phases were detected for the corresponding 2-phenylpyrimidine de rivatives. For the first time in the case of banana-shaped molecules a nema tic phase was observed for a 2'-nitro-m-terphenyl-4,4 "-diyl bisbenzoate. H owever, none of the synthesized compounds exhibit the typical texture of th e (anti) ferroelectric switchable mesophases, known from the Schiff's base derivatives.