Design And Assembly Of The Terpyridine-based Ligands Modified At 4 And 5 Position

In recent years,coordination-driven self-assembly has made great progress in the construction of supramolecular structures,including 1D helices,2D links,knots,macrocycles,3D capsules and cages.The application of supramolecules in catalysis,host-guest chemistry,light harvesting,light-emitting devices,gas storage,chemical separation and sensing has received a great deal of attention from scientists and has accelerated the active development of this research area.The generation of these supramolecular architectures requires good directionality and predictability in the selfassembly process.The design of the organic ligands and the predictable coordination of the transition metal ions involved in the self-assembly process is therefore put forward higher requests.Organic ligands are diverse and easily modifiable,and the synthesis of precise structures by modulating ligands has proven to be the most effective strategy for the development of coordination-driven self-assembly and related research fields.However,the development of ligands with high selectivity and recognition is still in its infancy.2,2’:6’,2’’-terpyridine as an NNN Pincer ligand play an important part in coordination chemistry due to their three coordination sites and low LUMO,their ability to form "closed-shell" octahedral < tpy-M-tpy> complexes,which provide a linear and stable bonds in supramolecular chemistry.So far,many discrete metal supramolecular structures based on terpyridine has been reported,like Sierpiński triangles,pentagons,hexagons,cubes,octahedral cages,etc.The self-assembly of terpyridine moieties as ligand still faces many problems as the size and complexity of the structures increase.The formation of unpredicted metallo-supramolecules significantly reduced the controllability of the assembly procedures.In multicomponent self-assembly,the terpyridine with similar coordination abilities often cause low coordination selectivity,which leads to the formation of unpredicted metallosupramolecules and significantly reduced the controllability of the assembly process.The selectivity and formation of the desired product can be significantly improved by introducing Ru(II)with stable linkage < tpy-Ru(II)-tpy>,but this leads to low yields of the expected product and difficulties in purification.However,it remains a great challenge to the synthesis of the simple and versatile terpyridine ligands with high coordination selectivity for diverse architectures and desired controllability.In this thesis,2,2’:6’,2’’-terpyridine compounds are used as the ligand,and discrete supramolecular structures are precisely constructed by modifying at 5,5’’ and 4,4’’ positions of two side pyridines and assembling them with different metal ions.The ligands and their corresponding supramolecules were characterized by electrospray ionization mass spectrometry(ESI-MS),ion mobility mass spectrometry(TWIM-MS)and nuclear magnetic resonance spectroscopy(1D 1H NMR,13 C NMR,2D 1H-1H COSY)techniques in four parts as follows.Chapter 1 Introduction to supramolecular chemistry and coordination-driven supramolecular self-assembly,the synthesis and modification of terpyridine ligand,the photophysical properties of terpyridine and their complexes,and the current development of 2D and 3D terpyridine supramolecular structures in recent years,then we propose the topic of this thesis.Chapter 2 Triphenylamine-modified 2,2’:6’,2"-terpyridine is used as the main ligand to investigate the synthetic method,and monotopic terpyridine ligands LA,LB,LC,LD,LE were designed and synthesized by 5,5’’ and 4,4’’(meta-and para-)modifications.By coordinating them with transition metal M(II)(M = Zn,Cd),a series of corresponding complexes MLA2,MLB2,MLC2,MLD2,and MLE2 are obtained and their structures are characterized using NMR spectroscopy and electrospray ionization mass spectrometry.The spectroscopic properties of the various complexes are also investigated considering that the terpyridine and triphenylamine moiety have been widely used in photoreceptors and organic light-emitting diodes in optoelectronic devices.Chapter 3 Having mastered the modification of the 5,5’’-and 4,4’’-positions through the synthesis in Part 2,we then proceeded to modify the terpyridine in these two positions.This part focuses on the modification of the terpyridine meta-position(5,5’’)and the multitopic terpyridine ligand LF and LG were designed and synthesised.The significant advantage of this design is that the terpyridine in the ligands have different chemical environments and show selective coordination with each other.For ditopic ligand LF,the self-assembly with Zn(II),Cd(II)and Fe(II)gave the rhombic dimer Zn2LF2,Cd2LF2,Fe2LF2 with the same terpyridine signal set as the ligand LF.The self-assembly behaviour of the tritopic ligand LG with Zn(II)and Cd(II)is observed for discrete tetramer Zn6LG4 and Cd6LG4 under thermodynamic control,while ligand LG and Fe(II)are assembled to generate a mixture of the tetramer,hexamer and octamer(Fe6LG4,Fe9LG6 and Fe12LG8),which are successfully isolated using regular chromatographic separation.In addition,the formation of discrete structures is facilitated by the formation of stable intermediates from ligands and metal ions.This is also demonstrated by mixing LG and Cd(II)with a precise stoichiometric ratio of 1:1.The above supramolecular complexes are thoroughly characterised by NMR spectroscopy,electrospray ionization mass spectrometry and 2D travelling-wave ion mobility-mass spectrometry.Chapter 4 Selective self-assembly of a single ligand is achieved,and in this section we continues a study of selective self-assembly in the case of multicomponent ligand.We design and synthesize the ligand LH,as isomers of LG,which is a tritopic ligand based on modification at para-positions(4,4’’)position of terpyridine.Self-assembly behaviour of LH is first investigated.Similar to LG,the self-assembly of LH with Zn(II)and Cd(II)is observed under thermodynamic control as discrete mixtures of Zn6LH4 tetramer and Zn9LH6 hexamer,Cd6LH4 tetramer.Subsequently,LG and LH are mixed and a sufficient amount of metal Zn(II)is added for a 1:1:3 assembly and it is found that the chaotic system does not show individual assembly but mutual coordination behaviour.The selective self-assembly is confirmed by NMR spectroscopy,electrospray ionization mass spectrometry and 2D travelling-wave ion mobility-mass spectrometry not only in single ligand systems but also in the case of multiple ligand commingling systems.