Novel nematic compounds incorporating two conjugated carbon-carbon double bonds in the terminal chain

The position and configuration of a carbon-carbon double bond strongly infl uence the transition temperatures, elastic and dielectric constants, viscos ity, birefringence, etc of nematic liquid crystals incorporating them. This behaviour can probably be attributed to conformational effects and anisotr opic pi electron density distribution and can be used to improve the optica l performance of STN-LCDs. However, relatively few liquid crystals incorpor ating two carbon-carbon double bonds have been reported([1-3]). Therefore, we have synthesised a wide variety of new compounds incorporating two conju gated trans-carbon-carbon double bonds in the same terminal chain. The effe cts on their physical properties on the presence of two double bonds have b een compared with those of the corresponding material either without a carb on-carbon double bond or with just one carbon-carbon double bond in the sam e position. Strong non-additive effects were found and of the dienes prepar ed exhibit high birefringence and nematic clearing points as well as being of surprisingly low viscosity.