Controlling the soft self-assembly of 1,3,4-oxadiazoles by carbosilane end-groups

Abstract

Herein we report the soft self-assembly of 1,3,4-oxadiazoles with carbosilane end groups in a series of polar and mirror-symmetry broken liquid crystalline (LC) phases. Most compounds are based on the new 4-[4-(5-hydroxyphenyl)-1,3,4-oxadiazol-2-yl)]benzoate building block and involve carbosilane end-groups. Compounds combining one silylated and one alkylated end form a sequence of lamellar, modulated lamellar and columnar phases with developing polar order and even leading to soft ferroelectrics. Silyl groups at both ends gives rise to a modulated lamellar phase with temperature induced transition to a hexagonal columnar phase, with the first observation of a polar switching in a columnar phase based on the oxadiazole heterocycle. Spontaneous mirror symmetry breaking (“dark conglomerate”) is observed after removal of the silyl group(s). The tilt correlation mode of the lamellar phases is controlled by combining a cyano-substituted with a silylated end. Overall, this work contributes to the understanding of the soft self-assembly of oxadiazole based and silylated bent-core mesogens, presenting new properties and potentiality for the oxadiazole materials. Also, it provides general guidelines for the targeted molecular design of functional soft matter with tailored morphologies and properties.