The synthesis and evaluation of ferroelectric liquid crystal host materials

Komandla, Srinivas Reddy

Abstract

This research is based on the synthesis and evaluation of liquid crystalline host materials for use in ferroelectric liquid crystal devices. The liquid crystal materials are synthesised by incorporating silane bulky end groups linked by an alkoxy spacer to a fluoroterphenyl molecular core.

The main aim of the research is to improve the alignment quality with the ultimate aim of bookshelf alignment. Almost as important is the target of wide temperature range, high tilt, and low melting SmC phase materials, but maintaining the low rotational viscosity of the fluoroterphenyl core.

The syntheses are reported of a series of silane compounds with bulky terminal groups attached to mono-, di-, and tri-fluoroterphenyl cores. The initial targets contain a pentamethyldisilane end group, but the route was unsuccessful so simpler targets with a butyldimethylsilane bulky end groups were prepared. The key part of the synthesis involves hydrosilylation, low temperature directed lithiation and Suzuki-Miyaura coupling reactions. The report discusses the syntheses and transition temperatures obtained from DSC and thermal polarising optical microscopy. The trends in the transition temperatures, and tilt angles of derived FLC materials, values are discussed and compared to literature compounds.

An exemplar is the addition of a chiral dopant (BE8OF2N) to butyl(6-((4''-((10- (butyldimethylsilyl)decyl)oxy)-2',3'-difluoro-[1,1':4',1''-terphenyl]-4-yl)oxy)hexyl)dimethylsilane 30a produces a high SmC* tilt angle of around 45° which varies little with temperature and there is a step in Ps data. This example 30a is mixed in percentages up to 50% with a model difluoroterphenyl KC1020 substituted in the middle ring. The bulky end group suppresses the N and SmA phase when compared to the dialkyl mesogen. A marked reduction in crystallisation temperature shows eutectic behaviour which is promising for ferroelectric mixture formulation. The same example 30a mixed with KC1019, fluorinated on the end ring, has similar behaviour, but with more support of the SmC phase. Other silane materials are mixed with KC1020 only, and their phase behaviour is discussed. Selected 50% mixtures of 30a+KC1019, 30a+KC1020, and an end ring monofluoroterphenylbutyldimethylsilane 39+KC1020 are doped with 7% w/w of standard dopant BE8OF2N(-S) aimed at the ideal phase sequence I-N*-SmA*-SmC*-C. The SmC* tilt angles are close to the ideal value of 22.5° at room temperature but Ps values vary.

Citation

Komandla, S. R. The synthesis and evaluation of ferroelectric liquid crystal host materials. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4217874

• Thesis Type: Thesis
• Deposit Date: Apr 22, 2016
• Publicly Available Date: Feb 23, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4217874
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Oct 1, 2015