Synthesis And Photoelectric Properties Of Novel Aggregation-Induced Emission Materials Based On Transition Metal Complexes

Recently,transition metal complexes as phosphorescent materials have attracted much attention due to their high emission efficiency,photo-and thermal stabilities as well as relative long excited lifetime.Therefore,phosphorescent materials are promising for the various applications such as electroluminescence devices,chemosensors,photocatalytic water reduction and cell imaging.However,transition metal complexes usually suffer from low luminescence efficiency in the solid or aggregatiton state,due to aggregation-caused quenching(ACQ).This drawback in phosphorescent materials significantly limits the real-world applications of these luminophores.Therefore,research and development of highly efficient solid-state luminescenct materials are still the focus of related work.In 2001,Tang et al.reported a novel compound named 1-methyl-1,2,3,4,5-pentaphenylsilole,which emits weakly when dispersed in good solvent and shows strong emission when aggregated or in the solid state.Tang et al.named this kind of anti-ACQ phenomenon ‘aggregation-induced emission'(AIE).This discovery gave a tremendous push for the development of highly efficient solid emission materials used in electroluminescence devices,chemosensors and cell imaging.However,up to now,the most reported AIE molecular are fluorescent molecular.Transition metal complexes-based aggregation-induced phosphorescent emission(AIPE)materials are relative rare.On the other hand,most of AIE materials have been found to possess piezochromic luminescence(PCL)property,which have attracted considerable interest in various fileds of applications,including optical recording and strain-or pressure-sensing systems.Thus,design and synthesis of new AIPE materials and study their photo-electric performances are significant to expand the application prospect of highly efficient luminescent materials.In this paper,we design and synthesize a series of new cationic Ir(III)and Cu(I)complexes,and their photophyical properties have been investigated in detail.All the relative studies are outlined as follows.1.Two Schiff-based ligands 1 and 2 were prepared by the simple and mild reaction in high yield.The synthesis of two dinuclear complexes 1 and 2 were achieved by 2-phenylpyridine cyclometalated iridium chloro-bridged dimer reacting with Schiff-based ligands 1 and 2,respectively.Detailed photophysical studies of complexes 1 and 2 are performed.The results revealed that two dinuclear ionic Ir(III)complexes are all highly efficient red emitters with AIPE property for the first time.Combining the crystal analysis with theoretical calculation results,it is clear that the nature of the flexible Schiff-based ligands in dinuclear complexes play a fundamental role in adjusting the luminescence properties,and this finding should be a versatile strategy for obtaining highly efficient solid-state luminescent materials for future applications.2.Tuning the emission color of complexes by decorating the cyclometalated chloro-bridged dimer without changing the Schiff base bridging ligands,we get two new dinuclear complexes 1 and 2 with orange emission.The detail photophysical studies of complexes revealed that both dinuclear ionic Ir(III)complexes are AIPE-active and simultaneously show reversible piezochromic luminescence(PCL)property for the first time.NMR spectra,powder X-ray diffraction(PXRD)and differential scanning calorimetric(DSC)data are presented.It is proposed that the flexible imine units of the Schiff base bridging ligand play an important role in achieving AIE,while the phenylpyrazole groups lead to simultaneous piezochromism.Developing new Ir(III)complexes with versatile and flexible bridging ligands hold great promise as a new strategy to achieve highly efficient piezochromic materials in the future.It is shown that complex 2 provides a fast-responding re-writable phosphorescence data recording device which makes both complexes competitive as candidates for practical applications.3.Based on our pervious studies,two new dinuclear cationic Ir(III)complexes with AIPE character had been obtained.We first constructed a rapid,highly sensitive and selective phosphorescent sensor for dangerous perchlorate in aqueous media by AIPE-active dinuclear cationic iridium(III)complexes.As a novel phosphorescent probe,two complexes could also efficiently detect perchlorate in living cells.NMR spectra,MS,crystal analysis and theoretical calculation results revealed that the anion-exchange induced AIPE is crucial for the large phosphorescence enhancement in the detection of perchlorate.These studies pave the way for a new efficient turn-on phosphorescence-based detection strategy for anions.4.We design and synthesize two new AIE-active cationic Cu(I)complexes with simultaneously show thermally activated delayed fluorescence(TADF)character.That emit weakly when dispersed in good solvent and show strong emission when aggregated or in the solid state.Luminescence decays experiments revealed that the strong emission of complexes in the aggragatiton state is originated from TADF.To further investigate the reason of TADF in the aggregation state,we doped the complexes with two different matrix(molecular weight)host materials(PMMA),detailed photophysical results,single crystal analysis and theoretical studies point to a direct evidence for the first time that effectively restrict the single molecular vibration through intermolecular interaction is a unique reason for TADF in the aggregation state.Taking advantages of TADF character in the aggregation state,we constructed an undoped OLEDs by using Cu(I)complexes as luminescent layer.Near 100 % exciton utilization efficiency originating from TADF is realized in the nondoped OLEDs which is hard to realize in ever reported non-doped OLEDs work.This finding may open novel photoelectron applications by this kind of emitter,in particular,for nondoped OLEDs.