Physical Properties of Nematic Tolans

Abstract

Abstract A series of 4-n-alkyl-4′-n-alkoxytolans, trans-4-n-alkylcyclohexyl-4′-n-alkyltolans and 4-n-alkyl-2′- or 3′-substituted 4′-n-alkoxytolans was prepared. Their mesomorphic and physical properties were measured. Some nematic mixtures of 4-n-alkyl-4′-n-alkoxy-tolans and other familiar series of nematic mixtures of two-ring systems having n-alkyl and n-alkoxy as terminal groups were prepared and their physical properties were compared. A nematic mixture of tolans has a high N-I transition temperature of 72[ddot]C, a high birefringence of 0.297 and a low viscosity of 19.1 c.p. at 20[ddot]C. The birefringence and the flow-aligned viscosity of trans-4-n-propylcyclohexyl-4′-n-butyltolan were determined by extrapolation and compared with those of trans-4-n-pentylcyclohexyl-4′-ethylbiphenyl and 4-n-propylphenyl 4′-n-propylcyclohexyl-benzoate. The influence of the introduction of 2′-, 3′-fluoro and 2′-, 3’ -methyl groups into 4-n-alkyl-4′-n-alkoxytolans on the dielectric constants was discussed.