Synthesis,Recognition And Chirality Sensing Of Naphthalene-based Flexible Endo-functionalized Molecular Cages

Supramolecular chemistry is an important branch of chemistry research.Macrocyclic host compounds are important tools for studying supramolecular chemistry.Compared to macrocyclic hosts,molecular cages with three-dimensional cavities usually have unique physical and chemical properties and better host-guest binding performance.Particularly,organic covalent molecular cages constructed by covalent bonds tend to have better dynamic stability than those cages that are constructed through metal coordination or dynamic covalent bonds.Covalent molecular cages reported in literature,usually have either flexible or rigid structure.Rigid structure is pre-organized,and undergo small or no conformational changes in the process of host-guest binding,reducing unfavorable entropic cost.However,too rigid structure requires guest molecules must perfectly fit the cavities of the cages in terms of size,shape and electrostatics.Otherwise,the binding will be seriously weakened.Certain degree of flexibility would permit the cavity to induced-fit according to the structure of guests.This would be good for a tight and strong host-guest binding.Entropic penalty due to conformational change would be compensated by enthalpic gain through better host-guest interactions with more binding sites.Under the guidance of this concept,we designed a new flexible molecular cages with multiple electron-rich aromatic sidewalls.The ether bonds were used to connect two benzene rings with three aromatic sidewalls to form the target molecular cages.Flexible ether bonds can give the molecular cage a certain degree of freedom to adjust its conformation,and the oxygen atoms on the ether bonds are possible to direct toward the cavity(“endo-functionalized” concept).So that additional interactions with the guests may form.Herein,we reported the molecular cage in line with the above design concept--a 2,3-naphthol-based cage(so-called “2,3-naphthocage”,or “2,3-NC” for short).Structural characterizations of 2,3-NC and its recognition behavior to organic cations were studied in detail,and the applications of 2,3-NC in high sensitivity detection of various organic cations and chiral sensing were explored as well.