Chirality-induced supramolecular nanodishes: enantioselectivity and energy transfer

Abstract

Self-assembly is one of the most important issues of fabricating materials with precise chiral nanostructures. Herein, we constructed a chiral assembly system from amphiphiles containing hydrophobic/hydrophilic chiral coils bonded to hexabiphenyl, exhibiting controllable enantioselectivity over various aggregation behaviors. The chiral coils aroused various steric hindrances affecting intrinsic stacking tendency and compactness, leading to different aggregating behaviors, as concluded from the self-assembly investigation. The strong π–π stacking interaction between the long hexabiphenyl groups gave rise to a relatively compact arrangement in the aqueous solution, whereas the methyl side groups on the coil segments raised steric hindrance at the rigid-flexible interface, resulting in loose stacking and formation of nanostructures with a larger curvature. Compared with the achiral molecule 1 that formed micron-sized large sheets, molecules 2–4 containing chiral coils aggregated into nanodishes, which looked exactly like mosquito-repellent incense, to overcome surface tension. The helical structures effectively amplified chirality and exhibited strong circular dichroism (CD) signals, which indicate enantioselectivity. In addition, the relatively loose packing behavior permitted their co-assembly with a dye and aided efficient energy transfer, providing a foundation for the chiral application of supramolecules. Thus, by introducing a simple methyl side group in amphiphilic molecules, asymmetric synthesis and energy transfer efficiency can be realized.