Enantiomers Self-Sort into Separate Counter-Twisted Ribbons of the Fddd Liquid Crystal─Antiferrochirality and Parachirality

Abstract

The recently discovered orthorhombic liquid crystal (LC) phase of symmetry Fddd is proving to be widespread. In this work, a chiral hydroxybutyrate linkage is inserted into the molecular core of hexacatenar rodlike compounds, containing a thienylfluorenone fluorophore. In addition to more usual tools, the methods used include grazing-incidence X-ray scattering, modulated differential scanning calorimetry (DSC), flash DSC with rates up to 6000 K/s, and chiro-optical spectroscopies using Mueller matrix method, plus conformational mapping. Although pure R and S enantiomers form only a strongly chiral hexagonal columnar LC phase (Col h *), the racemic mixture forms a highly ordered Fddd phase with 4 right-and 4 left-handed twisted ribbon-like columns traversing its large unit cell. In that structure, the two enantiomers locally deracemize and self-sort into the columns of their preferred chirality. The twisted ribbons in Fddd, with a 7.54 nm pitch, consist of stacked rafts, each containing ∼2 side-by-side molecules, the successive rafts rotated by 17°. In contrast, an analogous achiral compound forms only the columnar phase. The multiple methods used gave a comprehensive picture and helped in-depth understanding not only of the Fddd phase but also of the "parachiral" Col h * in pure enantiomers with irregular helicity, whose chirality is compared to the magnetization of a paramagnet in a field. Unusual short-range ordering effects are also described. An explanation of these phenomena is proposed based on conformational analysis. Surprisingly, the isotropic−columnar transition is extremely fast, completing within ∼20 ms. A clear effect of phase on UV−vis absorption and emission is observed.

Continuous Spectrum of Morphologies and Phase Behavior across the Contact Zone from Poly(l-lactide) to Poly(d-lactide): Stereocomplex, Homocrystal, and Between

“…This phase consists of adjacent right- and left-handed helical columns containing separated pure chiral enantiomers. While the racemic high-temperature columnar phase forms from the melt within 20 ms, the local deracemization and formation of the Fddd phase take 20 s . In this case, the rate-determining step is unpairing, while in the PLA case, it is pairing.…”

Chiral structures in azobenzene‐containing systems: Construction, regulation, and application

“…Similar to the precise chiral recognition in biomolecules, controlled chiral communication and expression are essential in many self-assembled systems, such as self-assembled small molecules, [6] helical polymers, [7] supramolecular polymers, [8] and liquid crystals (LCs). [9][10][11] Meanwhile, dynamic control of chiral structures is important for the development of functional chiroptical materials, which are essential for the specific functions. [12][13][14][15] This also enables it to show promising applications in the fields of chiral recognition, asymmetric catalysis, chiral modulation, enantiomeric sensors, and LC materials.…”

“…In addition, the precise construction and artificially controllable regulation of chiral structures would be expected to enable dynamic control of the corresponding biological functions. Similar to the precise chiral recognition in biomolecules, controlled chiral communication and expression are essential in many self‐assembled systems, such as self‐assembled small molecules, [6] helical polymers, [7] supramolecular polymers, [8] and liquid crystals (LCs) [9–11] . Meanwhile, dynamic control of chiral structures is important for the development of functional chiroptical materials, which are essential for the specific functions [12–15] .…”

Supertwisted Chiral Gyroid Mesophase in Chiral Rod‐Like Compounds

“…Recently we found that similar chiral compounds bearing six chains form a LC phase of coexisting straight right-and left-handed helical columns, spacegroup Fddd. [26] However, the Fddd formed only if both R and S enantiomers were present and not in pure enantiomers. Thus a similar situation may be expected in the gyroid cubic, with its coexisting right and left-handed networks, since in a pure enantiomer 50 % of molecules would have to enter the network of "wrong" chirality.…”

“…With two or more end-chains these so-called polycatenars may form either a network-based LC phase with 3D long-range order [13][14][15][16][17][18][19] or a columnar phase with 2D [20][21][22][23] and sometimes 3D order. [24][25][26] The 3D network phases are formed of 2 [2,12] or 3 [27,28] infinite interpenetrating nets-see Figure 1. The network segments are columns made up of stacked "rafts", each containing 2-4 molecules lying side-by-side perpendicular to the column axis (Figure 1c).…”