Highly birefringent nematic liquid crystals for reflective STN applications

An important parameter of any LCD containing portable electronic device is a low power requirement, The reflective STN display mode offers a moderate to high information content display with low power consumption, One method to realise colour in this mode is to use a large retardation (d Deltan) val ue in the cell. For a cell gap of 6 mum, and a retardation of similar to1.5 , a birefringence (Deltan) of greater than +0.2 is necessary. To achieve su ch a value in an STN LC mixture, materials with broad nematic range, good s olubility and a Deltan value of < +0.25 are required. A study of the trans-cyclohexyldifluorophenyltolane core structure was made and a large number of dialkyl, alkenyl-alkyl and alkoxy materials were syn thesised and characterised. These materials possess low to moderate melting points, broad purely nematic mesophases. a high Deltan and very good solub ility in nematic LC hosts. They are suitable materials for inclusion in mix tures for colour reflective STN displays.