Twist-bend nematic liquid crystals based on thioether linkage

Abstract

We developed twist-bend nematogens based on cyanobiphenyl dimers with thioether or sulfur linkage, as opposed to the commonly used methylene and ether linkages. Based on the smaller bond angle of thioether C–S–C than methylene C–CH₂–C and ether C–O–C, we designed two dimer homologous series that are more bent, symmetric CBSnSCB with two thioether linkages and asymmetric CBSnOCB with a thioether and an ether linkage, containing odd carbon numbers n = 3, 5, 7, 9, and 11, and also synthesized even-n members n = 6 for each system. Both CBSnSCB with n = 3, 5 and 7 and CBSnOCB with n = 5 and 7 formed a broad range of twist-bend nematic (N_TB) phases that were stable down to room temperature and showed remarkably enhanced glass-forming ability. In addition, CBS9OCB also formed N_TB phase at a fast scan rate. DFT calculations revealed that twist-bend nematogens CBS7SCB and CBS7OCB have smaller bend angles made of the para axes of the two cyanobiphenyl moieties and larger dipole moments than those of the conventional nematogen ether-linked CBO7OCB.