Dark conglomerates of domains with opposite handedness, which are designated dark conglomerate phases (DC phases), have attracted much attention. We prepared an achiral liquid crystal trimer, 4,4'-bis{9-[4-(5-octyloxypyrimidin-2-yl)phenyloxy]nonyloxy}biphenyl (I-9), and investigated the physical properties. A droplet of trimer I-9 formed a conventional nematic phase on cooling from the isotropic liquid, and then changed to an optical isotropic phase with homochirality. X-ray diffraction measurements reveal that the isotropic phase has an intercalated layer structure with a correlation length of 95 nm. We prepared binary mixtures with a nematic liquid crystal, 4'-hexyloxy-4-cyanobiphenyl (6OCB). The mixtures containing 30-75 mol % of 6OCB exhibited smectic phases above the isotropic phase. We investigated mesogenic properties of trimer I-n (n = 5-9) depending on the parity of the linking group. Only trimer I-9 possessing the longest odd-numbered spacers showed the chiral isotropic phase, suggesting that a rigid bent structure is not necessary for the appearance of the isotropic phase. The experimental results reveal that trimer I-9 exhibits a soft crystalline DC phase representing a new modification of chiral symmetry breaking in lamellar liquid crystal phases.

Dark conglomerates of domains with opposite handedness, which are designated as dark conglomerate phases (DC phases), have attracted much attention. After designing an achiral liquid crystal trimer, 4,4′-bis{7-[4-(5-octyloxypyrimidin-2-yl)phenyloxy]heptyloxy}biphenyl (1), which exhibits only a nematic phase, we prepared binary mixtures with some typical rod-like nematic liquid crystals, i.e., 4′-hexyloxy-4-cyanobiphenyl (6OCB), 2-(4-hexyloxyphenyl)-5-pentyloxypyrimidine (PPY), or 4-methyloxyphenyl 4-hexyloxycyclohexanecarboxylate (PCA), and investigated their phase transition behaviour. The binary mixtures containing 55–90 mol% of 6OCB were found to exhibit a nematic phase and a DC phase of chiral domains with opposite handedness. However, neither PPY nor PCA induced such a chiral conglomerate phase in the mixture with trimer 1. We discuss how core–core interactions contribute to produce such a chiral conglomerate phase.

Chirality's effects on physical properties of materials and how chirality arises have persisted as attractive issues in chemistry. We prepared a homologous series of achiral liquid crystal trimers in which three phenylpyrimidine units are connected via flexible heptamethylene spacers. An equimolecular mixture of a trimer with a nematic (N) phase and that with smectic A (SmA), smectic C (SmC), and smectic B phases was found to exhibit an N phase, a SmC phase, and a B4 phase composed of chiral domains with opposite handedness. The chiral characteristics of the B4 phase were confirmed by uncrossing the polarizers in opposite directions. XRD measurements reveal that both SmC and B4 phases have an interdigitated layer structure. That molecular interdigitation might form a supermolecular bent configuration that can produce saddle splay curvature to drive the B4 phase.

Chiral conglomerate phases have attracted much attention not only for the spontaneous mirror symmetry breaking but also for their nanostructures. We investigated both surface and bulk structures of a homologues series of an achiral liquid crystal trimer I-(n,m) exhibiting soft crystalline chiral conglomerate phases by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The trimers were found to form bicontinuous networks. In particular, trimer I-(9,9) exhibited a single gyroid-like surface accompanying periodic distribution of dimples with a size of about 100 nm. It showed a sponge-like structure in the bulk of the material. The twist conformation of the flexible trimer I-(n,m) can cause layer deformation, which produces bicontinuous networks exhibiting optical activity.