Two Cholesterol-Containing Pyrene Derivatives: Subtle Spacer Difference, Diverse Stimuli-Responsive Luminescence, Chirality, and Self-Assembly Behaviors

Two chiral molecules <b>1</b> and <b>2</b> were designed and synthesized with a pyrene moiety directly linked to a chiral cholesterol moiety and connected through a methylene spacer, respectively. Influence of the spacer on their stimuli-responsive luminescence, chirality, and self-assembly behaviors was systematically investigated. Molecules <b>1</b> and <b>2</b> had similar aggregation-induced emission enhancement (AIEE) in solution, because of carrying the same fluorescence moiety. Both molecules displayed mechanochromism (MC) property but with different color contrast, whereas only <b>2</b> showed mechanoluminescence (ML) activity. When doping in liquid crystal molecule 5CB, both molecules induced the formation of chiral nematic liquid crystals (N*-LCs) with strong circularly polarized luminescence (CPL). Molecule <b>2</b> induced single handedness signal, irrespective of doping ratios, while <b>1</b>-doped N*-LCs showed an inversion of CPL signal from negative to positive upon the increase of doping ratios. Molecules <b>1</b> and <b>2</b> also self-assembled into different coassemblies with 5CB. Their distinct behaviors were attributed to the influence of the methylene spacer, which caused different molecular conformation and steric bulkiness; accordingly, it changed intermolecular interactions and molecular packing of the two molecules and led to diverse chirality and luminescence. This work provided important model molecules to better understand the molecular structure-property relationship and guide the design of novel functional molecules.