Tuning the liquid crystal behavior of subphthalocyanines: effects of substitution, chirality, and hydrogen bonding

Abstract

Bowl-shaped aromatics that self-assemble into columnar liquid crystals (LCs) are key components for developing polarized semiconductors. However, progress in this field has been sluggish, as the limited set of available π-conjugated curved scaffolds has left structure–property relationships poorly understood. Herein we investigate the role that substitution pattern, substituent nature, and chirality play in the LC columnar organization of subphthalocyanines (SubPcs). Remarkably, we reveal that enantiopure SubPcs exhibit a reduced tendency to form liquid crystalline phases compared to their racemic counterparts, whereas higher substitution density increases flexibility within the columns, compromising coaxial alignment. Moreover, we find that the use of conformationally flexible, π-extended peripheral substituents enables efficient π–π stacking, and that the incorporation of hydrogen-bonding amide groups leads to highly stable mesophases with elevated melting points, although the mesophase remains at room temperature after thermal treatment. These trends are further rationalized through theoretical modeling. Overall, this work provides valuable synthetic and design guidelines for advancing bowl-shaped aromatics toward next-generation functional columnar liquid crystals.