Synthesis of fluorinated terphenyl liquid crystals with 3-propylcyclopentane end group

Abstract

High performance liquid crystal (LC) displays require nematic mixtures with low rotational viscosity to reduce the response time and large dielectric anisotropy to reduce the threshold voltage. Furthermore, liquid crystals (LCs) with low melting temperature and high clearing temperature are particularly attractive for automobile and outdoor display applications. In this article, we report a series of new fluorinated terphenyl LCs with 3-alkylcyclopentane end group. The terphenyl mesogen is designed for high Δn value, and the lateral fluorine atom is used to reduce the melting temperature. In comparison with the terphenyl analogue containing a 4-alkylcyclohexyl end group, discussed in previous works, the obtained LCs show wider nematic temperature range and smaller rotational viscosity because 3-alkylcyclopentyl moiety is introduced. The effect of alkyl chain length and the lateral fluoro substituent on the mesomorphic properties of the obtained LC is discussed. The results show that the nematic temperature range increases with the alkyl chain length increase. The position of the lateral fluoro substituent also plays an important role; LC with the fluoro substitution on the central benzene ring provides the widest nematic temperature range. In conclusion, we have synthesised a new series of LCs with low melting point, wider nematic temperature range and high Δn value, which is promising in formulating eutectic mixture for display application.

Keywords:

• terphenyl liquid crystals
• cyclopentyl end group
• fluoro substituent
• birefringence