High Birefringence Phenyl Tolane Positive Compounds For Dual Frequency Liquid Crystals

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 \u3c 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. © 2009 Taylor & Francis