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

摘要

The position and configuration of a carbon-carbondouble bond strongly influence the transition temperatures, elasticand dielectric constants, viscosity, birefringence, etc of nematicliquid crystals incorporating them. This behaviour can probably beattributed to conformational effects and anisortropic #pi# electrondensity distribution and can be used to improve the opticalperformance of STN-LCDs. However, relatively few liquidcrystals incorporating two carbon-carbon double bound have beenreported ~[1-3]. Therefore, we have synthesised a wide variety ofnew compounds incorporating two conjugated trans-carbon-carbon double bonds in the same terminal chain. The effects ontheir physical properties on the presence of two double bonds havebeen compared with those of the corresponding material eitherwithout a carbon-carbon double bond or with just one carbon-carbon double bond in the same position. Strong non-additiveeffects were found and of the dienes prepared exhibit highbirefringence and nematic clearing points as well as being ofsurprisingly low viscosity.