Liquid Crystals from Shape-Persistent Porphyrin Stars with Intrinsic Free Space

A small library of shape-persistent, conjugated star-shaped liquid crystals (LCs) with a zinc porphyrin core was successfully synthesized. Different conjugated arms are attached in the meso-positions. The self-assembly is at the limit between liquid crystals and soft crystal phases owing to the space-filling requirement. A model indicates the formation of dimers in double helices. A remarkable mesogen with thiophene linked directly to the porphyrin core generates J-aggregates in solution, which persist in the solid state. In the liquid crystal the J-aggregates disappear but can be reversibly reobtained by solvent treatment.