Swallow-tailed polycatenars: controlling complex liquid crystal self-assembly and mirror symmetry breaking at the Lamellae-Network cross-over

Abstract

Controlling the spatial organization of π-conjugated molecules in soft systems is of importance for the design of new materials with application relevant optimized properties. Here, soft self-assembly of functional multi-chained π-conjugated 5,5′-diphenyl-2,2′-bithiophenes is investigated. Focus is on molecules with a 3,5-disubstitution pattern at one end and no or only a single chain at the other end. By elongation of the single terminal chain, a transition from lamellar phases to helical networks is observed. With lowering the temperature, the lamellar phase types change from smectic via hexatic to crystalline. In some cases, different kinds of orders are combined in a single uniform lamellar structure. Moreover, a transition from uniform (synclinic) to alternating (anticlinic) tilt in adjacent layers is observed with decreasing chain length or rising temperature, due to a change of the molecular conformation from tuning fork like to Y-shaped. For compounds terminated with a long chain, helical self-assembly of the π-conjugated rods in networks takes place, leading either to a racemic (𝐼𝑎3⎯⎯𝑑, gyroid) or a spontaneous mirror symmetry broken (I23) bicontinuous cubic phase and a chiral isotropic liquid phase (Iso1[*]) as well. This work establishes rules for controlling the self-assembly of functional π-conjugated rods in soft matter and fluids.