The synthesis and properties of liquid crystals for twisted nematic and ferroelectric displays

Hird, Michael

Abstract

This thesis is concerned with the synthesis, characterisation and physical properties of liquid crystal materials which (i) improve the switching speeds and multiplexability of twisted and supertwisted nematic display devices, (ii) exhibit the smectic C phase and are suitable for use as host materials for ferroelectric display devices, (iii) exhibit the nematic phase and have high polarisabilities and high optical anisotropies (birefringence).
(i) 4-Alkoxy- or 4-alkyl- 4'-cyanobiphenyls and 4-cyanophenyl 4-alkoxy- or 4-alkyl- benzoates have a positive dielectric anisotropy which is required to be large in order to provide fast switching speeds in twisted nematic display devices. The use of lateral fluoro-substituents can provide high dielectric anisotropies by breaking up antiparallel associations of the parent systems and by adding to the dipole. A range of fluoro-substituted cyanophenyl benzoate esters was prepared to provide dopants of high positive dielectric anisotropy and to provide information as to which fluoro-substitution patterns provide the most favourable results.
(ii) Ideal host materials for the ferroelectric display device are very difficult to obtain because of the need for low melting points, large smectic C ranges, low viscosities and large negative dielectric anisotropies. Excellent ferroelectric host materials have been prepared by utilising two ortho difluoro-substituents in terminal alkoxy- and alkyl- substituted l,T:4’,l"-terphenyls. This arrangement of lateral fluoro-substituents provides a narrow molecule which minimises viscosity and upholds smectic C phase thermal stability whilst providing a lateral dipole which leads to negative dielectric anisotropy.
(iii) A 2,6-disubstituted naphthalene moiety has been used in conjugation with an ethynyl linking group to give nematic materials of very high optical anisotropy.
The synthesis of the compounds included in this thesis required the development of extremely useful and interesting palladium-catalysed cross-coupling procedures including some novel selective couplings. This convergent approach to synthesis is very advantageous and provides high product yields.

Citation

Hird, M. (1990). The synthesis and properties of liquid crystals for twisted nematic and ferroelectric displays. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4223916

• Thesis Type: Thesis
• Deposit Date: Feb 11, 2022
• Publicly Available Date: Feb 24, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4223916
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Jan 1, 1990