A new series of nematic and smectic liquid crystals with negative dielectric anisotropy: the effect of terminal chain substitution on thermal and electro‐optical properties

Abstract

Two alkyl (1b and 1c) and four fluoroalkyl derivatives (1d–1f) of 4‐arylbutyric acid (1c, 1d and 1e) and 4‐arylbutanol (1b, 1f and 1g) [aryl = 2′,3′‐difluoro‐4′‐(2‐(E‐4‐pentylcyclohexyl)ethyl)‐biphenyl‐1‐yl] were prepared and investigated in the pure form as nematic materials (1b and 1c) and as additives to a ferroelectric liquid crystal (FLC) host (1d–1f). A comparison of 1b and 1c with the decyl analogue 1a demonstrates the effect of terminal chain modification on thermal and electro‐optical properties. The substitution of the –CH₂O– (1b) or –COO– (1c) for –CH₂CH₂– in 1a destabilized the N and SmA phases or completely eliminated the smectic behaviour (1c). Dielectric analysis revealed that the chain modification increased the negative Δε, reduced elastic constant K ₁₁ and moderately decreased rotational viscosity γ₁. The temperature dependence of the key electro‐optical parameters was analysed for ester 2, the methyl analogue of 1c, which exhibits a 45 K wide N phase. All four fluoroalkyl derivatives 1d–1f showed enantiotropic SmA phases and 1e also exhibited a monotropic SmC phase. Solutions of 1d–1f in a FLC host (0.2 mmol g⁻¹) increased the tilt angle Θ (up to 45° for 1g), reduced rotational viscosity γ₁ and the risetime τ. The most dramatic changes were observed for 1g, which contains 15 fluorine atoms.

Acknowledgements

Partial financial support for this work was received from the National Science Foundation (DMR‐0606317). We thank Dr Bill Thurmes of Displaytech for his generous gift of the MX 6146 host. We also thank Dr Wiktor Piecek for helpful discussions.

Notes

1. A by‐product, 2,3‐difluoro‐4‐(2‐(E‐4‐pentylcyclohexyl)ethyl)biphenyl, was isolated in 5% yield as a nematic oil with the clearing temperature of 39°C.