Ester-type banana-shaped monomers and investigations of their electro-optical properties

Abstract

New banana-shaped monomers 1a–1f, based on the 1,3-phenylene bis{4-[4′-(alkenyloxy)benzoyloxy]}benzoate bent structure were prepared. The central 1,3-phenylene ring was either unsubstituted (1a, 1b) or had a 2-methyl substituent (1c, 1d) or a 4-chloro substituent (1e, 1f), respectively. The occurrence of mesophases greatly depended on the chemical structure of the banana-shaped molecules. Whilst 1,3-phenylene bis{4-[4′-(10-undecenyloxy)benzoyloxy]}benzoate (1b, acronym Pbis11BB) formed a monotropic B2 phase, the 4-chloro derivatives showed conventional nematic and SmC phases. In contrast, the 2-methyl derivatives did not form any kind of mesophases. MOPAC/AM1 semi-empirical calculations allowed evaluation of the value and orientation of the electric dipole vectors and of the twist angles of the central phenyl ring with respect to the outer rings. Electro-optical investigations showed that the B2 phase of 1b was antiferroelectric with a 45° tilt angle between 91–75 °C (P = 320 nC · cm−2) and a switching time in the range of 50 μs in a E = 15 V · μm−1 field. Synthetic route for the preparation of monomers 1a–1f.