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)­phenyloxy­nonyloxy}­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.