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

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 (B7H) and a B7 low-temperature phase (B7L) 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. [ABSTRACT FROM AUTHOR]