Assembly And Emission Studies Of Coordination Supramolecules Containing Aggregation-Induced Emission Groups

Since Tang and others innovatively proposed the concept of aggregation-induced emission?AIE?,researchers have conducted a lot of explorations and researches on the AIE activity system.As a breakthrough study,the AIE phenomenon is completely contradictory to the aggregation caused quenching?ACQ?effect of conventional organic fluorescent materials.As the iconic AIE fluorophores,the basic emission mechanism and various applications of tetraphenylethylene?TPE?and 9,10-distyrylanthracene?DSA?have been widely explored.For a single AIE molecule,the energy of the excited state will be continuously consumed by the movement of the benzene ring,so it cannot generate fluorescence.But after forming aggregates,the restriction of intramolecular motion?RIM?can impede the path of nonradiative transitions,thereby inducing fluorescence emission through radiative transitions.In particular,AIE derivatives typically exhibit unique optical responses to external stimuli such as heat and pressure due to structural distortion and steric hindrance.Up to date,a series of discrete 2D large rings,3D cages,and other nanomaterials with well-defined size and shape have been constructed through coordination-driven self-assembly.Based on the unique optical behavior of AIE active molecules,a series of AIE molecules were introduced into the supramolecular systems,exhibiting various properties,such as sensing,imaging,recognition,and catalysis.For most of the reported discrete supermolecules containing AIE units,higher fluorescence quantum efficiency can be observed in the aggregate state,but they do not emit light or have weaker fluorescence in the solution state.This limits the application prospects of AIE active supramolecules in some extent.Therefore,we introduced two typical AIE units,TPE and DSA,into the supermolecules,and constructed the supermolecules that emit efficiently in the solution state.And through the precise control of the composition,distribution,and shape of the supramolecules can regulate the luminescence properties of the solution state and the aggregate state.The specific research contents are as follows:1.The ligands LA and LB were synthesized by the modification of terpyridine and TPE.These two ligands were assembled with metal Zn?II?to form two 3D supramolecular cages[Zn₆LA₃]and[Zn₆LB₃].The final structures were characterized by ¹H NMR,¹³C NMR,2D COSY NMR,2D DOSY NMR,electrospray ionization mass spectrometry?ESI-MS?and traveling-wave ion mobility mass spectrometry?TWIM-MS?.Photophysical properties were characterized by UV-Vis and fluorescence spectra.Compared with[Zn₆LA₃],the introduction of additional alkyne bonds in[Zn₆LB₃]can increase the structural rigidity and stabilize the molecular conformation,so we obtained supramolecular cage with high efficiency in dilute solution.A series of hybrid cages can be obtained by mixing LA and LB for assembly,and the fluorescence intensity was significantly increased with increasing content of LB.When the supramolecular solution was rapidly cooled into a glassy state,the rotation of TPE can be further restricted,resulting in a marked increase in fluorescence.Moreover,the fluorescence of ligands and supramolecules have responsiveness for external pressure.In particular,the fluorescence of[Zn₆LB₃]will gradually increase under low pressure.When the pressure exceeds 1.10 GPa,the fluorescence will gradually decrease until quenching.When the pressure was released,the supramolecular fluorescence will gradually recover.2.The“V”and“X”type ligands were successfully synthesized through the modification of pyridine and DSA.These two ligands were assembled with 120°di-Pt?II?ligand to form two2D supramolecular structures.The structures were characterized by ¹H NMR,³¹P NMR and electrospray ionization mass spectrometry?ESI-MS?.Photophysical properties were characterized by UV-Vis and fluorescence spectra.Although the building units of the two supramolecules are similar,the difference in the distribution of the light-emitting groups makes a higher fluorescence quantum efficiency of S2,which is 14.19%.And from the fluorescence spectra of supramolecules in mixed solutions of good solvents?DMSO?and poor solvents?H₂O?,it can be seen that increasing the proportion of water caused the molecules to aggregate and induced fluorescence enhancement,and the difference in the shape make the two supramolecules have different luminous intensities in the aggregated state.