High birefringence phenyl tolane positive compounds for dual frequency liquid crystals

Abstract

Dual frequency liquid crystals (DFLCs) provide a possibility to achieve sub-millisecond rise and decay times and are useful for various electro-optical devices. In most of DFLC mixtures, ester compounds are utilised in order to obtain a low crossover frequency. However, the ester linking group does not provide π electron conjugation so that the DFLC mixtures usually exhibit a limited birefringence (Δn < 0.3 at λ = 633 nm). For phase modulation a lower birefringence demands a thicker cell gap which, in turn, increases the response time and operating voltage. This problem becomes more severe as the wavelength increases. In this paper, we introduce a series of isothiocyanato phenyl tolane positive compounds with high birefringence and moderate dielectric relaxation frequency. The dielectric and electro-optical properties of these compounds are investigated. We also formulated a DFLC mixture using these new positive compounds which exhibits Δn = 0.39 at λ = 633 nm and 0.33 at λ = 1550 nm.

Keywords:

• high birefringence
• dual frequency liquid crystals

Acknowledgements

The authors are indebted to Professors R. Dąbrowski and X. Liang for their technical support and AFOSR for the financial support under Contract No. FA95550-09-1-0170.