Construction And Luminescent Properties Of Metallo-supramolecular Structures

In recent years,luminescent materials have attracted the attention of an increasing number of scientists due to their wide range of applications in biological imaging,chemical sensing,optoelectronics and other fields.Coordination-driven self-assembly has become a powerful strategy for the preparation of supramolecular structures due to its directionality and predictability.The introduction of fluorophores into ligands to produce luminescent supramolecular structures not only enriches and expands the family of fluorescent materials,but also often provides some new properties for luminescent materials.Among them,rational ligand design and precise fine-tuning are the difficulties and key points in constructing highly emissive or tunable luminescent materials.In this paper,three types of luminescent supramolecular structures have been obtained based on metal coordination assemblies,which have been fully characterised by NMR spectroscopy,electrospray mass spectrometry,ion mobility mass spectrometry,and crystal X-ray diffraction.The photophysical properties of the supramolecular structures were further explored,and their luminescence behaviour was tuned by different strategies,including their tunable emission wavelength,significantly enhanced fluorescence efficiency,and selective sensing properties.The research of the thesis is divided into four parts as follows.Chapter 1 An overview of supramolecular chemistry and coordination-driven self-assembly is presented.It summarises the two-dimensional and three-dimensional luminescent coordination supramolecular structures reported in recent years and presents the research ideas of this thesis in the light of the difficulties faced at this stage.Chapter 2 Four terpyridine-based tetraphenylethylene(TPE)ligands were designed and synthesised,distinguished by the presence of different substituents at the vertices,namely LA(without alkyl chains),LB(with eight methoxy substituents),LC(with eight hydrophilic C7 ether-oxygen chains)and LD(with eight hydrophobic C6 alkyl chains).Ligands were with an angle of 60° between the TPE core and four terpyridine units,and the ligands were assembled with Zn(II)to give four twisted prisms SA,SB,SC,and SD.The formation of the complexes was successfully characterized by NMR spectroscopy,electrospray mass spectrometry,and ion mobility mass spectrometry.The photophysical properties of the four twisted prisms were then further investigated in dilute solution and in the aggregated state.It was found that with the introduction of substituents at the vertices,the prismatic molecules exhibited varying degrees of tunable visible emission in both the aggregated state and in solvents of different polarities.In addition,the hierarchical self-assembly behaviour of prisms was explored.The prismatic SD formed left-and right-handed spiral nanofibres under hydrophobic interactions,while only spherical aggregates of different sizes were observed for the other three prismatic molecules.These results suggested that the introduction of substituents is a favourable strategy for achieving tunable fluorescence emission from supramolecules,where the introduction of multiple hydrophobic chain segments allowed for further different hierarchical self-assembly properties.Chapter 3 In this chapter,two trans and cis isomeric ligands of bipyridyl TPE(MA and MB)were firstly designed and synthesized,after assembled with 120°di-platinum(II)acceptor M1,two rhomboidal metallacycle isomers C1 and C2 were prepared.The rhombic metallacycle C1 constructed by the trans-TPE-based ligand MA had a curved conformation that restricted the molecular motion of the aryl benzene ring of TPE in dilute solution,enabling the binding of AIE and CIE and showing enhanced fluorescence quantum yields.In addition,C1 exhibited better fluorescence stability towards strongly electron-withdrawing groups.Subsequently,two 3D metallo-cages,C3 and C4,were further constructed by assembling TPA-based ligand with different diplatinum(II)acceptors.3D metallo-cages,due to their steric nature,are not only effective in increasing the degree of confinement of free rotating groups in dilute solutions,but also hinder π-π stacking in the solid state,allowing them to better exploit their fluorescence properties compared to 2D metallacycles.The work in this chapter demonstrates that suitable ligands combined with appropriate angles can achieve enhanced luminescence under conformational control,and also demonstrates that conformational control is an available means of imparting unique fluorescent properties to supramolecules.Chapter 4 Three bidentate ligands,L1-L3,with a fixed angle between the two ligatable pyridines but at different distances,were designed and synthesised to self-assemble with a 180° double platinum(II)acceptor of the 9,10-diphenylethene(DSA)group,respectively,to construct a series of "bow-tie" supramolecules S1-S3 with crossover characteristics,and the structures were confirmed by NMR and mass spectrometry.The chromophore DSAs of these complexes are arranged at a certain cross-angle,which is extremely favourable for the luminescence properties.During the study of the photophysical properties of these complexes,it was found that as the crossover angle increased,the crossover dipole stacking increased,the interaction between the leaping dipoles diminished and the fluorescence emission intensity and quantum yield increased.These studies suggest that tunable fluorescence emission of supramolecular materials can be achieved by adjusting the stacking pattern between chromophores.