Structure and molecular packing in smectic BCr and Ad phases of Schiff base liquid crystal compounds through the analyses of layer spacing, entropy and crystal structure

Yasuhisa Yamamura; Takahito Murakoshi; Sakiko Iwagaki; Natalia Osiecka; Hideki Saitoh; Mafumi Hishida; Zbigniew Galewski; Maria Massalska-Arodź; Kazuya Saito

doi:10.1039/c7cp03863a

Structure and molecular packing in smectic B_Cr and A_d phases of Schiff base liquid crystal compounds through the analyses of layer spacing, entropy and crystal structure

Phys Chem Chem Phys. 2017 Jul 26;19(29):19434-19441. doi: 10.1039/c7cp03863a.

Authors

Yasuhisa Yamamura¹, Takahito Murakoshi¹, Sakiko Iwagaki¹, Natalia Osiecka², Hideki Saitoh³, Mafumi Hishida¹, Zbigniew Galewski⁴, Maria Massalska-Arodź², Kazuya Saito¹

Affiliations

¹ Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
² The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Kraków 31-342, Poland.
³ Department of Chemistry, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan.
⁴ The Faculty of Chemistry, University of Wrocław, Wrocław 50-383, Poland.

PMID: 28718465
DOI: 10.1039/c7cp03863a

Abstract

Single-crystal structural analyses and heat capacity measurements were performed on two Schiff base liquid crystal compounds, 5CBAA (4-chlorobenzylidene-4'-pentyloxyaniline) and 5ABCA (4-pentyloxybenzylidene-4'-chloroaniline). The alkyloxy-chain of a 5CBAA molecule was conformationally ordered in the crystal at room temperature. While that of 5ABCA was partially disordered in the room temperature phase but ordered in a low-temperature phase at 100 K. The structural phase transition involving the disordering of the conformation was observed at 107 K in the heat capacity of 5ABCA. Both compounds showed two liquid crystalline phases, SmB_Cr and SmA_d. The net entropy change associated with the chain disordering was essentially the same in them despite the difference in the orientation of their central -CH[double bond, length as m-dash]N- moiety. The layer-spacings of SmB_Cr and SmA_d phases were analyzed for their chain-length dependence in both series of mesogens (nCBAA and nABCA), as well as in the case of nBBAA (4-bromobenzylidene-4'-alkyloxyaniline). The results reveal that these smectic structures are composed of alternately stacked core- and chain-layers with an antiparallel arrangement of cores and a bent-form of molecules.