The Theory And Application Of Novel Ring Metal Iridium Complexes

The ring metal iridium complex is a kind of novel metal-organic molecules formed by the coordination of conjugated organic molecules and iridous compunds.Compared with most luminescent organic molecules,this kind of ring metal phosphorescent complexes have excellent photoelectric properties and the photothermal stability of these complexes is obviously improved.Their emission color can be tunable by modifying the specific functional groups on the ligands.Thus,the study of the relationship between the structure,electron density distribution and the properties of of metal iridium complexes has a guiding effect on the synthesis of novel complexes with certain photoelectric properties.Generally,iridium complexes have large Stokes shift,relatively high phosphorescence emission efficiency and longer luminescence lifetime,which are widely applied in photochemical sensors,biological cell imaging,electrochemiluminescence sensors,catalytic decomposition catalysts and organic light-emitting diode.One of the fastest growing application is designed to be a photochemical sensor.Iridium complexes phosphorescent materials can be effectively used to avoid the interference of background stray light and intracellular autofluorescence.Thus,iridium complexes will obtain better chemical detection and biologic imaging effect by using time resolved technique in real sample or live cell imaging.Therefore,people have great interest in researching phosphorescent chemosensors with long phosphorescence lifetime and good biocompatibility.In this paper,a series of ring metal iridium complexes were synthesized and their structures,orbital energy distribution,electron density distribution,photophysical properties and their applications in chemical,biological sensing and cell imaging were studied in detail.The main work is as follows:1.The HOMO and LUMO orbit energy and electron density distributions of seven of iridium complexes were caculated by density functional calculation（DFT）: They are（pq-COOCH3）₂Ir（acac）（1）、（pq-COOH）₂Ir（acac）（2）、（pq）₂Ir（pic）（3）、（pq）₂Ir（cys）（4）、（pq）₂Ir（acac）（5）、[（pq）₂Ir（bpy）]⁺PF₆^–（6）和 [（pq）₂Ir（bpy-COOK）]+ PF6 –（7）,wherein pq is 2-phenylquinoline,pq-COOH is 2-phenylquinoline-4-carboxylic acid,pq-COOCH₃ is methyl 2-phenylquinoline-4-carboxylate,acac is acetylacetone,bpy is 2,2’-bipyridine,bpy-COOH is 4,4’-dicarboxy-2,2 ’-bipyridine.In order to verify the theoretical results,complexes（1）-（7）were synthesized and characterized by NMR and the optical,electrochemical properties of the complexes were studied.Compared with the experimental results,the neutral iridium complexes（4）and ionic complexes（7）have lower HOMO energy levels,inducing lower oxidation potential,which possess high fluorescence quantum yield and good electrochemical property.The quantum efficiencies were 0.390 and 0.2646,respectively,which were significantly higher than that of [Ru（bpy）₃]²⁺.These phosphorescent metal iridium complexes had high luminous efficiency and unique molecular structure,which could be designed as functional phosphorescent probes.2.Design and synthesize the molecular iridium complex（pq）₂Ir（cys）as a pH,mercury ion bifunctional sensor.In this section,iridium complex（pq）₂Ir（cys）was reported for the first time,and its structural properties were characterized by UV,photoluminescence,nuclear and magnetic resonance spectroscopy.The maximum absorption wavelength of the complex in the ultraviolet region is located at 275 nm and the maximum emission wavelength is located at 579 nm.The iridium complex with mercapto group formed new complex in the presence of mercury ions in that the original luminescence of（pq）₂Ir（cys）was quenched,with good sensitivity and selectivity.In addition,due to the stability of complex（pq）₂Ir（cys）and the high quantum yield of luminescence,phosphorescent iridium complex（pq）₂Ir（cys）shows “ON-OFF” property with the variation of environmental pH,which can be considered as a good pH sensor.3.A water-soluble ionic iridium complex [（pq）₂Ir（bpy-COOK）]⁺PF₆^-was synthesized,which had a good response to tryptophan.At the same time,the toxicity test and cell imaging experiment of the complex were carried out.The results showed that the iridium complex had low cytotoxicity and could stain the cytoplasm and nucleus,exhibiting excellent cell imaging capacity.On this basis,the phosphorescent probe was able to sensitively response to the change of tryptophan in the cells.Then,we combined the iridium complex with bovine serum albumin（BSA）in PBS to form Ir-BSA,and the phosphorescence intensity was significantly enhanced.The effect of different metal ions was also investigated by adding different metal ions to the obtained solution.It was found that only copper ions could reduce the enchanced phosphorescence signal.Thus,the complex（7）can effectively detect tryptophan,BSA and copper ions as an efficient phosphorescent probe.