Abstract
Helical structures continue to inspire, prompted by examples such as DNA double-helix and alpha-helix in proteins. Most synthetic polymers also crystallize as helices, which relieves steric clashes by twisting, while keeping the molecules straight for their ordered packing. In columnar liquid crystals, which often display useful optoelectronic properties, overall helical chirality can be induced by inclusion of chiral chemical groups or dopants; these bias molecular twist to either left or right, analogous to a magnetic field aligning the spins in a paramagnet. In this work, however, we show that liquid-crystalline columns with long-range helical order can form by spontaneous self-assembly of straight- or bent-rod molecules without inclusion of any chiral moiety. A complex lattice with Fddd symmetry and 8 columns per unit cell (4 right-, 4 left-handed) characterizes this “antiferrochiral” structure. In selected compounds it allows close packing of their fluorescent groups reducing their bandgap and giving them promising light-emitting properties.
Highlights
Helical structures continue to inspire, prompted by examples such as DNA double-helix and alpha-helix in proteins
In liquid crystals (LC), long-range order can generally be achieved more and quickly than in crystals, making them interesting for functional materials where order is required for their function
The high-T trigonal columnar phase of IC3/n compounds was described in ref
Summary
Helical structures continue to inspire, prompted by examples such as DNA double-helix and alpha-helix in proteins. We report a 3D LC phase where we show that homochirality of helical columns can propagate to long-range even without molecular chirality or network junctions. All compounds form a uniaxial columnar phase at higher temperatures, IC3/n with trigonal (Coltri)[32], and FCN16 and FO16 with hexagonal symmetry (Colhex), see Table 1, Fig. 1, Figures further below and Supplementary Figs.
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