Fig. 1.

(A) Structure of CB7CB [4′,4′-(heptane-1,7-diyl)bis(([1′,1″-biphenyl]-4″-carbo-nitrile))]. The end-to-end length of its van der Waals surface is ∼3.0 nm in the all-trans molecular configuration. (B) CB7CB molecule can be viewed as having three parts, each ∼1 nm in length: two rigid end groups connected by a flexible spacer. The nematic director field n(r) is the local average orientation of the n_i, the long axes of the rigid end groups, each contributing to n(r) at its red circles. (C) Schematic illustration of the heliconical TB structures in the layered chiral SmC* phase and in the layerless NTB phase. The NTB drawing is a qualitatively correct representation of the TB structure found in CB7CB, in which any interval along the helix of single pitch length p_TB ∼ 8 nm includes, on average, four overlaps of 1-nm-long rigid ends and four intervals of 1-nm-long flexible spacers.