Novel Nematic Compounds Incorporating Two Conjugated Carbon-Carbon Double Bonds in the Terminal Chain

Abstract

The position and configuration of a carbon-carbon double bond strongly influence the transition temperatures, elastic and dielectric constants, viscosity, birefringence, etc of nematic liquid crystals incorporating them. This behaviour can probably be attributed to conformational effects and anisotropic π electron density distribution and can be used to improve the optical performance of STN-LCDs. However, relatively few liquid crystals incorporating two carbon-carbon double bonds have been reported^[1–3]. Therefore, we have synthesised a wide variety of new compounds incorporating two conjugated trans-carbon-carbon double bonds in the same terminal chain. The effects on their physical properties on the presence of two double bonds have been compared with those of the corresponding material either without a carbon-carbon double bond or with just one carbon-carbon double bond in the same position. Strong non-additive effects were found and of the dienes prepared exhibit high birefringence and nematic clearing points as well as being of surprisingly low viscosity.

Key Words:

• dienes
• double bonds
• TN and STN-LCDs