Origin of the Monolayer and Bilayer Arrangement in Smectic A and C Mesophases and Nematic Cybotactic Domains: The Case Study of Benzyloxy-Terminated Isoxazole Liquid Crystals

Luana D. Lopes, Leonardo P. Pavan, Itamar L. Gonçalves, Paulo F. B. Goncalves, Francisco P. dos Santos, Adailton João Bortoluzzi, Fabrício Luiz Faita, Rafaela R. da Rosa, Aloir António Merlo

Research output: Contribution to journalArticlepeer-review

Abstract

The synthesis and characterization of two benzyloxy-terminated isoxazole liquid crystals, (ILCs) 7a (n-octyl) and 7b (n-decyl), are described. The synthesis of the five-membered isoxazole ring was based on the (3 + 2) 1,3-dipolar cycloaddition to furnish the isoxazoline cycloadduct and the subsequent MnO2-oxidation. The liquid crystal (LC) behavior was accomplished by polarized optical microscopy (POM), differential scanning calorimetry, single-crystal X-ray diffraction, X-ray diffraction (XRD), 7-lithium nuclear magnetic resonance (7Li-NMR), and density functional theory (DFT) calculations. For both ILCs, the nematic cybotactic (Ncyb) and smectic A and C mesophases were characterized. Two organizational monolayer and bilayer regimes for the smectic A and C mesophases were characterized by the XRD pattern, and the Ncyb mesophase was assigned by the analysis of the low intensity of the peak at 2θ = 2.70°, suggesting some smectic character for the nematic mesophase. A correlation length (ξ) of around 20 layers and 7 layers was established by XRD for the monolayer and bilayer organization in the SmC mesophase. Single-crystal XRD, 7Li-NMR experiments, and DFT calculations were performed and are discussed in the context of the LC behavior influenced by the benzyloxy-terminated group. A model for the layering organization is presented as well as the organization in the Ncyb, SmA, and SmC mesophases.

Original languageEnglish
Pages (from-to)3113-3127
Number of pages15
JournalCrystal Growth and Design
Volume23
Issue number5
DOIs
Publication statusPublished - 3 May 2023

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