Molecular curvature and the twist-bend liquid crystal phases: the effect of the spacer

The synthesis and characterisation of ten members of the 4[{[4({5[4((4-cyanophenyl)phenyl]oxy)pentoxy}yl)phenyl]methylidene}amino] phenyl 4-alkyloxybenzoates is presented. These dimers are referred to using the acronym CBO5OIBeOm in which m refers to the number of carbon atoms in the terminal chain and varies from 1 to 10. The CBO5OIBeOm series exhibits nematic (N), twist-bend nematic (NTB), and smectic A (SmA) phases depending on the length of the terminal chain. Although the NTB phase is observed, these dimers do not exhibit the twist-bend smectic C (SmCTB) phases. By comparison, the structurally similar CB6OIBeOm series does exhibit the SmCTB phases, and this strongly suggests that the formation of the SmCTB phase is more sensitive to molecular curvature than that of the NTB phase.