High birefringence lateral difluoro phenyl tolane liquid crystals

Abstract

Four laterally difluorinated phenyl tolane liquid crystals were synthesised and their physical properties evaluated. These compounds exhibit a fairly small heat fusion enthalpy (ΔH ∼ 12.56 kJ mol⁻¹), which is favourable for mixture formulations. For comparison, four lateral difluoro cyclohexane tolane homologues are also studied. We doped 10 wt% of each compound into a commercial negative mixture N1 and measured the birefringence, visco-elastic coefficient and figure of merit. Birefringence varies very little between homologues, but the visco-elastic coefficient increases as alkyl chain length increases. The refractive indices of these guest–host mixtures at 1550 nm are also measured.

Keywords:

• high birefringence
• negative dielectric anisotropy
• liquid crystals

Acknowledgement

The authors are indebted to the Air Force Office of Scientific Research (AFOSR) for financial support under Contract No. FA95550-09-1-0170.