Helicity, assembly, and circularly polarised luminesence of chiral AIEgens

As opposed to most fluorophores that suffer from aggregation-caused quenching (ACQ), aggregation-induced emissive luminogens (AIEgens) possess very weak fluorescence in solution, but show strong emission upon aggregation due to restriction of intramolecular motion (RIM). Since AIEgens are often comprised of propeller-shaped structures, i.e. polyphenylsiloles or tetraphenylethylene (TPE), the attachment of chiral units has recently proven a powerful tool to fabricate chiral AIEgens exhibiting strong circularly-polarized luminescence (CPL) signal upon aggregation. Different chiral moieties lead to various assembled structures, such as helical nanoribbons, superhelical ropes, hollow and solid micro-/nanospheres. Generally, these structures exhibit enhanced chiroptical properties when compared to their monomeric counterpart. In this context, we report on the tetraphenylsilole and TPE derivatives with side-chains bearing an enantiomerically pure chiral units readily assembled into superhelical ropes upon aggregation, which displayed large CPL dissymmetry factors (g_em) of –0.32 – a record for purely organic chiral materials.