Selenium-linked liquid crystal dimers for twist-bend nematogens

The recently discovered twist-bend nematic (N-TB) phase has become an intensively studied topic in supramolecular chemistry and condensed matter science. Herein, a new molecular design for twist-bend nematogens employing the selenoether (C-Se-C) linkage, instead of the conventional methylene or ether linkages, is introduced. We synthesized CBSenSeCB dimers, consisting of two cyanobiphenyl (CB) units connected by two selenoether linkers sandwiching an odd-numbered alkylene spacer (n = 3, 5, 7, and 9) and revealed their phase transitions and mesomorphism. CBSenSeCB (n = 5, 7, and 9) can potentially form mesophases; notably, CBSe7SeCB formed the N-TB phase from the conventional uniaxial nematic phase, which was cooled to below room temperature. The structure of the all-trans model of CBSe7SeCB, optimized by the density functional theory, suggests that the molecular bend angle between the para axes of the cyanobiphenyl moieties is (similar to)90 degrees, which is more bent than those of previously reported twist-bend nematogens. Such a keen curvature is ascribed to the small C-Se-C angle of (similar to)101 degrees. In addition, the molecular bend angles of the twist-bend dimers, including the present and previously reported ones, correlate linearly with their phase-transition temperatures. The present study paves the way for the molecular design of new twist-bend nematic liquid crystals based on chalcogen linkages. (C) 2019 Elsevier B.V. All rights reserved.