Supramolecular liquid crystals exhibiting a chiral twist-bend nematic phase

Abstract

A selection of novel, chiral supramolecular liquid crystals formed by hydrogen-bonding are reported and their phase properties characterised by polarised optical microscopy, X-ray diffraction and resonant soft X-ray diffraction. Their behaviour is compared to that of their achiral analogues. The binary mixture of the bent-shaped, non-mesogenic H-bond acceptor 1OB6OS and chiral H-bond donor (S)-(2-Me)4OBA exhibits chiral nematic (N*) and chiral smectic A (SmA*) phases. Doping the twist-bend nematogenic (N_TB) complex 1OB6OS:4OBA with (S)-(2-Me)4OBA in ternary mixtures induces a transition from the N* phase to the chiral twist-bend nematic phase N*_TB, the first example seen in a supramolecular liquid crystal. The binary mixture of CB6OS and (S)-(2-Me)4OBA exhibits N* and N*_TB phases, with the helical structure of the latter having a periodicity of approximately 2 complex lengths (∼8 nm). The nature of the hydrogen bond is reversed in a binary mixture of the bent-shaped, twist-bend nematogen CB6OBA with (S)-(2-Me)4OBA, and this exhibits the phase sequence N*–N*_TB–SmC*–SmX.