Construction And Emission Properties Of Terpyridine-based Supramolecular Structures

Coordination-driven self-assembly is a method to construct discrete supramolecular structures by the coordination bond formed between organic ligands and metal ions.During the assembly process,the coordination bonds formed by the ligands and metal ions can undergo self-correction,eventually obtaining a thermodynamically stable supramolecular structure.Because ligands can be designed with functional groups,it greatly enriches the structure of coordination supramolecular and can endow it with expected functions.In recent years,luminescent tunable supramolecular materials have received extensive attention,a large number of structurally diverse and tunable luminescent supramolecular structures have been prepared by combining precise structure of coordination supramolecular with luminescent units and has shown applications in several fields,such as imaging,catalysis.In this article,a series of two-dimensional(2D)and three-dimensional(3D)luminescent coordination supramolecular structures were designed based on the 2,2’:6’2"-terpyridine(tpy)unit.The supramolecular structures were characterized by nuclear magnetic resonance(NMR)and electrospray ionization mass spectrometry(ESI-MS),and their luminescent properties were studied.The article mainly includes the following three parts:Chapter 1 The research progress of coordination-driven supramolecular assembly and the design strategy of luminescent supramolecular structures were introduced.Based on the current problems in the construction of luminescent supramolecular structures,the research content of the article was proposed.Chapter 2 This section designed tritopic terpyridine ligands LA and LB with1,3,5-triazine units,which were coordinated with Zn(II)to assemble supramolecular prisms SA and SB.The composition of the supramolecular structures was proved by NMR and ESI-MS,and the size of the supramolecular structures was determined by TEM and AFM.In addition,the photophysical properties of supramolecular prisms in solution,aggregation state,and solid state were studied.The SA without alkyl chains had strong emission in acetonitrile and solid state,with fluorescence quantum yields(Φ_F)of 39.20%and 16.22%,respectively.When adding water as a poor solvent to the acetonitrile solution of SA,the fluorescence intensity showed a slight increase and then a decrease with the increasing proportion of water,and the formation of nanospheres composed of SA was observed by TEM.However,SB with 12 alkyl chains almost did not emit light in solution,withΦ_Fof only 0.07%.But it emited orange fluorescence in the solid state,and the emission efficiency was significantly improved,withΦ_Fof 10.59%.With the increase of aggregation degree,the fluorescence intensity of SB continued to increase,and nanorod aggregates were formed.This section constructed triazine-based supramolecular prisms with efficient luminescence in the solid state,and found that the introduction of alkyl chains will seriously affect the luminescence of supramolecular in solution.Chapter 3 Building on Chapter 2,this chapter focuses on the effect of substituent positions on supramolecular fluorescence.Based on ortho-substituted terpyridine ligands,axisymmetrical tetratopic ligands were obtained by modifying the alkyl chains at the top and side positions of the ligands.These ligands were then assembled with Zn(II)to form triangular macrocycles S1,S2,and S3,which were structurally characterized by NMR,ESI-MS,and TWIM-MS.By studying the photophysical properties of the triangular macrocycles,it was found that S1(both positions with alkyl chains)and S2(only the top position with two alkyl chains)were weakly fluorescent in both solution and solid states compared to S3(no alkyl chain at the top position but with two at the side position).The fluorescence properties of the dimeric model compounds of S1,S2,and S3 in solution also matched these results.Further enriching the types of substituents and introducing different electron-donating and electron-withdrawing groups,it was found that the presence of electron-donating substituents at the top position resulted in a decrease in fluorescence efficiency,while electron-withdrawing substituents had little effect on the fluorescence efficiency of the assemblies in acetonitrile.