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

Full Paper: New banana-shaped monomers 1a-1f, based an 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 B-2 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/AMI 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 45degrees tilt angle between 91-75degreesC (P = 320 nC . cm(-2)) and a switching time in the range of 50 mus in a E = 15 V . mum(-1) field.