Rod-like liquid crystals of organic transition-metal complexes. Part 4.—Optically positive uniaxial nematic phase in the bis[1-(4′-alkoxybiphenyl-4-yl)-3-alkylpropane-1,3-dionato]copper(II) complexes

Abstract

We report that the long-alkoxy-chain substituted bis(β-diketonato)copper(II) complexes, bis[1-(4′-dodecyloxybiphenyl-4-yl)-3-alkylpropane-1, 3-dionato]copper(II)[alkyl substituent (R′): ethyl, n-propyl and n-butyl], show a nematic (N) phase. The methyl complex has a discotic rectangular ordered columnar (D_ro) phase, as reported previously. Therefore, the change from the D_ro phase to the N phase occurs with changing from R′= methyl to R′= ethyl groups. In order to obtain derivatives having a wider temperature range for the nematic phase, a homologous series of the bis[1-(4′-alkoxybiphenyl-4-yl)pentane-1,3-dionato]copper(II) complexes (alkoxy = C_nH_{2n+ 1}O; n= 6, 8, 10, 11, 14) have been synthesized for R′= ethyl. The derivative for n= 11 gave the widest range (ΔT= 16.1 °C). Furthermore, the nematic phase of these complexes was established as an optically positive uniaxial nematic phase. The mesomorphism of the corresponding ligands was also investigated.