Novel nematic and chiral nematic liquid crystalline materials for use in applications

The design, synthesis and characterisation of novel liquid crystal materials for emerging applications presents many challenges. The physical property parameters become ever more stringent and corresponding exceptional property liquid crystalline compounds are required. Two topics have been researched; high birefringence (Δn), high photo and chemical stability nematic materials for PDLC/AMD use and chiral nematic (N*) photopolymerisable compounds for polymer network formation. Many materials were designed, synthesised and characterised for each application and materials were found that were very suitable for each application.Materials for PDLC/AMD use, should be low melting, high Δn nematogens. Additionally, these materials should possess a high degree of chemical and photostability. The synthesis and characterisation of compounds containing N-heterocyclic rings, naphthalene rings or lateral fluorosubstituted p-terphenyl moieties in combination with different endgroups is described. The study demonstrated that N-heterocyclic rings produce a high Δn but are not sufficiently photochemically stable. 2,6-naphthalene containing terminal chloro substituted compounds were shown to have high Δn and high stability but also had high melting points. Lateral fluoro substituted, alkyl p-terphenyls with fluoro, chloro, thiomethyl and methoxy had low melting points, broad nematic mesophases and high stability and were very suitable for PDLC/AMD use.The study of N* photopolymerisable compounds for polymer network formation examines the design, synthesis and characterisation of both mono and diacrylates, monoepoxides and monovinylethers in combination with a range of chiral centres. The (S)-(+)-2-methylbutyl group when in combination with various mesogenic cores was found to be very useful as the chiral portion in low melting point enantiotropic N* monoacrylates, monoepoxides and monovinylethers. These compounds were also found to be eminently suitable for the formation of binary mixtures with nematic diacrylates, divinylethers and diepoxides. These mixtures showed visible wavelength selective reflection and could be photopolymerised into coloured chiral polymer network films.