4-Methylresorcinol based bent-core liquid crystals with azobenzene wings – a new class of compounds with dark conglomerate phases

Abstract

Stochastic achiral symmetry breaking in soft matter systems, leading to conglomerates of macroscopically chiral domains (so-called dark conglomerate ¼ DC phases) is of contemporary interest from a fundamental scientific point of view as well as for numerous potential applications in chirality sensing and noncentrosymmetric materials. Herein we report the synthesis and investigation of first azobenzene containing bent-core mesogens derived from 4-methylresorcinol forming DC phases with a new structure, distinct from the known fluid sponge-like distorted smectic phases as well as from the helical nano-filament phases (HNF phases, B 4 phases). The effects of chain length and other structural modifications on achiral symmetry breaking were investigated. Homologues with relatively short alkyl chains form achiral intercalated lamellar LC phases (B 6 phases), but on increasing the chains, these are replaced by the chiral and optically isotropic DC phases. Compounds with the longest alkyl chains form low birefringent crystalline conglomerates which represent less distorted versions of the optically isotropic DC-phases. Introducing additional peripheral substituents at both outer rings removes the DC phases. The DC phases were also removed and replaced by modulated smectic phases if the azo groups were replaced by ester units, showing that azo groups favour DC phase formation with new nanostructures, distinct from the previously known types.

Polar Order, Mirror Symmetry Breaking, and Photoswitching of Chirality and Polarity in Functional Bent‐Core Mesogens

“… Synthetic route to the bent‐core mesogens AB n , A F B16 , AT n , and A F T16 : i) SOCl 2 , DMF, reflux 1 h; ii) Et 3 N, pyridine, CH 2 Cl 2 , reflux, 6 h; iii) H 2 , 10 % Pd/C, THF, stirring, 48 h at 25 °C; iv) 1) H 2 NOH, 2) Ac 2 O, 3) NaOH.…”

Chiral conglomerates observed for a binary mixture of a nematic liquid crystal trimer and 6OCB

“…The N to DC phase transition was confirmed by the texture change. 23,24 Layer spacing in the previously reported HNF phases is usually close to the molecular length. S3.…”

Double gyroid structures made of asymmetric dimers

“…Above the cubic phase the isotropic liquid exhibiting very strong density fluctuations was found; similar phenomenon has been lately observed for other mesogens forming 3D structures. [39,40] Most probably, the isotropic liquid with strong fluctuations is a sponge [41] phase or cubosome [42] type phase. By opening access to a new class of materials forming double gyroid structures our findings may be beneficial for alignment-free and solution-processable electronic devices.…”