Supramolecular Networks: Helical Networks of π‐Conjugated Rods – A Robust Design Concept for Bicontinuous Cubic Liquid Crystalline Phases with Achiral Ia3¯d and Chiral I23 Lattice (Adv. Funct. Mater. 45/2020)

Abstract

In article number 2004353, Goran Ungar, Carsten Tschierske, and co‐workers present a general design concept of bicontinuous cubic liquid crystals consisting of helical networks that are stable over a broad temperature range. Increasingly bulky substituents cause increasing helical twist between the three‐chain 2,2′‐bithiophene based molecular rods, resulting in a sequence of three distinct phases: two ranges of achiral double network (Iatrue3¯d) separated by a range of spontaneously chiral triple network (I23).

Controlling Mirror Symmetry Breaking and Network Formation in Liquid Crystalline Cubic, Isotropic Liquid and Crystalline Phases of Benzil‐Based Polycatenars

“…On cooling compound 4/14 , as example, a broad feature occurs in the DSC traces in the temperature range of the isotropic liquid phase, indicating a liquid state polyamorphism (liquid–liquid transitions, see Figure 3). [9b,38,44,46, 49a] The additional sharp peak at the transition to the cubic phase is associated with a sudden change from fluidity to viscoelasticity. The majority of the enthalpy of this Iso–Iso 1 –Cub bi transition is involved in this broad feature (6–7 kJ mol −1 ) which is interpreted as a growth of aggregates which fuse to a network structure and continuously increases network connectivity (Iso 1 phase), [38a,44, 49a] being in line with recent results of 1 H‐NMR diffusion and relaxation studies [49b] .…”

“…Tiny chirality sources are also assumed to be responsible for “spontaneous” formation of I 23 [ * ] or Iso 1 [ * ] phases with uniform chirality, as observed in some cases [8] . However, for the benzil‐based compounds the tendency to form large homogeneous chiral domains is less developed if compared with related 2,2′‐bithiophene based polycatenars [29a, 46] and formation of relatively small chiral domains is dominating in this class of compounds (see Figures 2 a–c and 9 a–d). A possible reason could be a higher viscosity or the bent molecular shape, slowing down the growth processes.…”

“…Notably, there are two distinct type of I a d phases, occurring on either side of the I 23 [ * ] phase, a long pitch (low twist) I a d (L) and a short pitch (high twist) I a d (S) phase, leading to the phase sequence I a d (L) – I 23 [ * ] – I a d (S) with growing twist between the molecules along the networks [44–46] . In previous work we have shown that these rod‐like molecules do not only form mirror symmetry broken cubic phases, mirror symmetry breaking is in some cases even observed in the adjacent isotropic liquid phases (Iso 1 [ * ] ), forming liquid conglomerates [45, 47] .…”

Swallow‐Tailed Polycatenars: Controlling Complex Liquid Crystal Self‐Assembly and Mirror Symmetry Breaking at the Lamellae‐Network Cross‐Over

“…[ 23 ] There is also a Cub bi phase with more complex triple network structure (previously designated as Im m ) which is only formed in systems involving rod‐like units, the polycatenars being the most prominent, and different models are under discussion, as will be described in Section 3.6. [ 24–26 ] The recent discovery of helix formation, spontaneous mirror symmetry breaking, optical activity and enormous chirality amplification effects, observed in some of the Cub bi phases, [ 27–32 ] in the adjacent non‐cubic tetragonal [ 33 ] and the isotropic liquid phases (Iso 1 [ * ] ) of these achiral polycatenar compounds [ 34–36 ] has renewed the interest in this class of compounds. [ 37–39 ] Such spontaneously chiral soft matter systems are of potential technological interest and might also be of importance for the understanding of the mechanism of emergence of uniform chirality.…”

“…In this work we explore structural modification of 5,5′‐diphenyl‐2,2′‐bithiophene‐based polycatenar compounds [ 27a,28,29,33,34a ] and we establish the fundamental understanding of these effect on the mesogenic self‐assembly at the crossover from lamellar phases to helical networks. The study focuses on new series of compounds with an 3,5‐disubstitution pattern at one end and being either non‐terminated ( B m /H ) or terminated with only a single alkyl chain at the other end ( B m / n and B′6/ n ).…”