Structural investigations on B₇ phases of new bent-core mesogens including a binary system

Abstract

Twelve new five-ring bent-core compounds have been synthesised which are derived from 2-nitroresorcinol and which contain only ester linkage groups. Their mesophase behaviour was investigated by polarising microscopy, X-ray diffraction and electro-optical measurements. It was found that most of the compounds studied form a B₇ phase. For several compounds, a phase transition between a B₇ high-temperature phase (B_7H) and a B₇ low-temperature phase (B_7L) was clearly detected by calorimetry, by a small change of the texture and by X-ray diffraction measurements. For one compound, (A12), well-aligned samples were obtained which allowed a more detailed structural characterisation of the B₇ phases. Interestingly, by fast cooling of the isotropic liquid, the same compound forms a metastable columnar phase. Furthermore, the binary system composed of the compound A12 and a member of the B₇ parent series was investigated. X-ray diffraction measurements give evidence that the B₇ phases of both mixing components are completely miscible, i.e. they belong to the same phase type.

Keywords:

• bent-core mesogens
• B₇ phases
• X-ray diffraction
• binary system