Leveraging Torsional and Steric Strains: A Pre‐macrocyclization Strategy Enables Conformation‐Specific Fullerene Binding in m‐Cyclophanes

Abstract

AbstractThough the chemistry of resorcinarenes is half a century old, the conformationally‐locked resorcinarene crowns are generally constructed using hydrogen bonds or covalent tethers. Often, covalent tethering involves extra post‐macrocyclization steps involving upper‐rim functionalities. We have leveraged the torsional and steric strains through α‐substituents of the lower‐rim C‐alkyl chains and accomplished conformationally‐rigid fluorescent m‐cyclophane deep‐crowns in a predetermined way. The strategy offers a pre‐macrocyclization route conserving upper‐rim functionalities, an aspect overlooked in resorcinarene chemistry. X‐ray structural and computational analyses unveil the cause for conformational rigidity in m‐cyclophanes due to α‐branching in C‐alkyls (linear vs. α‐/β‐branched). The conformationally‐locked fluorescent deep‐crown with a preorganized cavity captures hydrophobic spherical guest C60 in both solution and solid states specifically, when compared to conformationally‐dynamic boats, enabling conformation‐specific binding.