Supramolecular Host-Guest Systems Based On Cyclometalated Platinum(?) Complexes

Supramolecular chemistry is a subject that studies the formation of highly-ordered molecular assemblies through non-covalent interactions between two or more chemical species.In contrast with the strong covalent bond of traditional molecular chemistry,supramolecular chemistry is focused on the weak non-covalent interaction.Non-covalent interactions can be classified into different categories,such as hydrogen bonding,metal coordination,?-? stacking,metal-metal interaction and so on.The dynamic reversibility of non-covalent interactions imparts the supramolecular systems with stimulus responsiveness,which lays the solid foundation for the application of supramolecular assemblies in areas such as chemical sensing,biological imaging,drug delivery,and supramolecular catalysis.In this respect,exploring novel non-covalent interactions and functional supramolecular systems is the hot research topic in supramolecular chemistry.Owing to the intriguing optical properties and the controllable intramolecular or intermolecular Pt(?)Pt(?)metal-metal interaction and ?-? stacking,cyclometalated platinum(?)complexes have emerged as one special supramolecular building block.In recent years,bis[alkynylplatinum(?)]polypyridyl molecular tweezer/guest supramolecular system have been developed by our group.In this regard,the research content of this thesis are focused on the host-guest chemistry,and self-assembly of cyclometalated platinum(?)complexes.In detail,the research work can be divided into four chapters.Based on the fact that a variety of research work were focused on the study of N^N^N cyclometalated platinum(?)complexes,we endeavor to change the charge of cyclometalated platinum(?)species and design N^N^C cyclometalated platinum(II)complexes to study their host-guest complexation behaviour in the first chapter.The results demonstrate that the molecular tweezer on the basis of N^N^C cyclometalated platinum(?)motif shows different emission spectra in comparision with the mononuclear platinum(?)counterpart,which originates from intramolecular interaction of molecular tweezer in the excited state.Moreover,the auxiliary ligand of guest have only minor effects on the host-guest chemistry between molecular tweezer and the respective guest.In the second chapter,macrocyclization strategy is a common approach to enhance the preorganization of synthetic receptors,we try to evaluate the different host-guest properties induced by two preorganized synthetic receptors(macrocycle and molecular tweezer).In this respect,two alkynylplatinum-based host—guest systems with structurally similar macrocycle and molecular tweezer have been designed and synthesized.Moreover,the discrepancies of macrocycle/guest and molecular tweezer/guest have been investigated.Two-fold bonds tend to form for macrocycle/guest complex,while only one-fold Pt(?)-Pt(?)bond exists for molecular tweezer/guest complex.As a result,macrocycle/guest complex displays one order of magnitude higher for the non-covalent binding affinity,and 3-fold enhancement for the photosensitized than molecular tweezer/guest complex.In the third chapter,owing to the novelty and excellent optical property of Pt(?)---Pt(?)metal-metal interaction,we try to design stimulus responsive molecular tweezer and apply tweezer-directed supramolecular system to control this novel non-covalent interaction and supramolecular polymerization process.In detail,the pH changes can induce the conformation variation of molecular tweezer from "U' to "W"via the formation of two-fold intramolecular N-H---O hydrogen-bond,which leads to the release of guest and the dispearance of Pt---Pt metal-metal interaction.Futhermore,the t mixture of two supramolecular monomers in equivalent manner lead to the formation of the macroscopic supramolecular polymer and the self-assembly behaviour also can be controlled by pH change.In the fourth chapter,in view of the fact that the two dependent species exist in common supramolecular host-guest systems on the basis of N^N^N cyclometalated platinum(?)complex,we try to design new molecular tweezer and supramolecular momomer,and explore their self-association behaviour and cation responsiveness.In detail,the planar and cation ter:pyridine encasuplates into the cavity of molecular tweezer,which leads to the formation of self-association molecular tweezer via four-fold ?-? stacking in many organic solvent.Moreover,the addition of Zn(?)and competing ligand can control the process of self-association and supramolecular polymerization.