systems are important building blocks in supramolecular assembly because of their versatile noncovalent interactions with various functional groups. Particularly,  ,  and  interactions are widely used in supramolecular assembly and recognition.
 concerns the direct interactions between two -systems; and  interaction arises from the electrostatic interaction of a cation with the face of the -system. Unlike these two interactions, the  interaction arises mainly from charge transfer between the C–H orbital and the -system.