Crystal and mesophase structure of a bicyclohexyl cyano mesogen

The phase behaviour of 4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]benzonitrile, C22H31N, 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.

Source: Acta Crystallographica Section C - October 24, 2022 Category: Chemistry Authors: Gupta, S. Das, P.P. Crispini, A. Scarpelli, F. Borbone, F. Centore, R. Tags: mesogen texture crystal packing ordered smectics crystal structure benzonitrile research papers Source Type: research