Crystal and mesophase structure of a bicyclohexyl cyano mesogen. Issue 11 (24th October 2022)

• Record Type: Journal Article
• Authors: Gupta, Sakuntala; Das, Partha Pratim; Crispini, Alessandra; Scarpelli, Francesca; Borbone, Fabio; Centore, Roberto
• Is Part Of: Acta crystallographica. Volume 78:Issue 11(2022)
• Page Start: 647
• Page End: 652
• Publication Date: 2022-10-24
• Subjects: mesogen -- texture -- crystal packing -- ordered smectics -- crystal structure -- benzonitrile; Crystallography -- Periodicals; Crystals -- Periodicals; 548.3
• DOI: 10.1107/S2053229622010105
• Languages: English
• ISSNs: 2053-2296

Abstract

Abstract : 4‐[ trans ‐4‐( trans ‐4‐Propylcyclohexyl)cyclohexyl]benzonitrile has two different solid phases and exhibits thermotropic liquid‐crystalline behaviour, with a remarkable interval of stability of the mesophase between the lower melting solid phase (75 °C) and the isotropization temperature (247 °C). Abstract : The phase behaviour of 4‐[ trans ‐4‐( trans ‐4‐propylcyclohexyl)cyclohexyl]benzonitrile, C22 H31 N, 1, has been examined. This compound has two different solid phases, denoted I and II, and exhibits thermotropic liquid‐crystalline behaviour, with a remarkable interval of stability of the mesophase between the lower melting solid phase (75 °C) and the isotropization temperature (247 °C). The crystal and molecular structures of solid phase I have been determined at 173 K. The cyclohexyl rings both adopt the chair conformation and are equatorially substituted. The packing of 1 in the crystalline state is driven by the antiparallel arrangement of cyano dipoles with the formation of close contacts involving the strong cyano acceptor and weak aromatic C—H or aliphatic C—H donors. The crystal packing is discussed and compared with X‐ray diffraction data in the liquid‐crystalline state. The combination of thermal analysis, optical polarizing microscopy and X‐ray diffraction analysis suggests that the mesophase is a partially ordered smectic phase. The lamellar structure of the mesophase is retained in crystalline solid phase II obtained by cooling the liquid‐crystalline phase.