Invited Lecture. Material properties, structural relations with molecular ensembles and electro-optical performance of new bicyclohexane liquid crystals in field-effect liquid crystal displays

Abstract

Several new classes of polar and non-polar bicyclohexane liquid crystals comprising alkenyl side chains are presented. The compounds exhibit low optical anisotropies, Δn, < 0.1 and rotational viscosities, γ₁, as low as 35 cP at 22°C. This leads, in combination with large elastic expressions k = k ₁ + (k ₃ - 2k ₂)/4 > 12 × 10⁻¹² N, to low viscoelastic ratios γ₁/k and to short response times in field-effect liquid crystal displays (LCDs). Strong odd-even effects occur in the bend/splay elastic ratio k ₃/k ₁ upon shifting the alkenyl double bond from even into odd side chain positions. As a result the ratio k ₃/k ₁ can be tuned over the wide range 0·9 ≲ k ₃/k ₁ ≲ 3·0. Correlations between the electro-optical properties of twisted nematic, supertwisted nematic, optical mode interference LCDs and material parameters demonstrate the high degree of multiplexability of the new compounds. Roche interactive molecular modelling is applied to determine the possible equilibrium configuration not only of single molecules, but for the first time to whole molecular ensembles comprising 12 molecules. First results show that the shape of the ensembles, E, depends on the position of the double bond in the side chains of the molecules. The length/width ratio of E decreases for even double bond positions.