Unraveling planar chirality in pillar[5]arenes

Pillar[5]arenes have attracted considerable interests in the areas of supramolecular chemistry, material science and stereochemistry. However, they likely encounter a challenge in obtaining stable enantiomers due to the presence of rotational single bonds in the cavity structure, instead leading to a high predisposition to racemization. This review summarizes approaches that have been developed to address this issue by effectively constraining their free rotation, including the introduction of bulky substituents and formation of mechanical interlock structures. The controllable flipping behavior of chiral bismacrocycles with pillar[5]arenes as the core is reviewed under the stimulation of external environment. Moreover, we will discuss the application areas that rely on the planar chirality of pillar[5]arene, such as circularly polarized luminescence, molecular recognition, and chiral organic nanotubes.