Theoretical Study On The Excited State And Spectral Properties Of Iridium (?) And Platinum (?) Complexes Phosphorescent Materials

Phosphorescent transition metal complexes(PTMCs)with excellent photophysical properties and rich electronic structure have become a hotspot research field in information display,information storage,bioimaging and biological detection.Transition metal complexes usually have some specific photoelectric properties.The introduction of iridium,platinum and other transition metal elements has led to better utilization of radiative emission of the triplet state exciton and achieved efficient phosphorescence emission,which has attracted a lot of scholars interested in research.The platinum atoms exhibit d8 electron configuration,so the platinum(II)chelate with the coordination atoms is a planar coordination compound of four coordination.Iridium(III)complexes with the electronic structure of d6 are octahedral geometry,with a short triplet life and excellent luminescent performance,and become the most widely used phosphorescent material in the field of electroluminescence.In recent years,long-lived PTMCs have been applied for biosensing and bioimaging.The long emission lifetime is associated with the rich properties of excited states.The thesis focuses on these issues,and analyzes the geometric and electronic structures of the ground state and excited state of transition metal complexes by quantum chemistry method,and explains the luminescence properties of the complexes,so as to reveal the relationship between the structure and properties of the complexes.The main contents of this paper are as follows:1.Hypochlorite is one of the important reactive oxygen species in the organism and plays an important role in immune activity.However,excessive hypochlorite will lead to a series of diseases,such as arthritis,neuronal disease,lung injury.Therefore,it is of great significance to realize its in-situ detection in living cells.An iridium(III)complex with octadecyl chain and oxime group was designed and synthesized.The octadecyl chain in the complex has a target cell membrane function.The oxime group could be used as a hypochlorite reaction group to construct an open hypochlorous acid probe that targets a cell membrane.The iridium(III)complex showed weak luminescence before addition hypochlorite.When reacted with hypochlorite,the oxime group is oxidized by hypochlorite to form carboxyl group,the quenching effect disappeared and the phosphorescence was emitted,which shows the specificity of hypochlorite.However,it is difficult to explain the change of the excited state properties of the complex before and after the detection and the change of the photophysical properties caused by the experiment.In order to understand the principle in more details,the effects of the complexes before and after the reaction with hypochlorous acid(oxime group to carboxyl group)were studied by density functional theory(DFT)and time-dependent density functional theory(TD-DFT)the relationship between the spin-orbit coupling and the radiation rate and non-radiation rate was investigated.The results showed that the phosphorescence emission efficiency of the complex can be reasonably explained and predicted by theoretical calculation,and the theoretical basis for the understanding of the detection principle of the complex probe is provided.2.Hypoxia is associated with a variety of diseases,such as cardiovascular disease and tumors.Therefore,accurate determination of oxygen in biological systems is important for the diagnosis and treatment of disease.Because of its unique triplet excited state properties,PTMCs have attracted wide attention in the field of chemical induction and biomimetic imaging,such as high luminous efficiency,long emission life,good light stability and large stokes displacement.The energy transfers between the long-lived triplet excited state complex and the triplet state molecular oxygen caused by the diffusion-controlled collision interaction can quench the phosphorescence intensity of the complex and shorten the emission lifetime of the complex.So PTMCs in the chemical induction and biological imaging has become a wide area of concern.In the experiment,four iridium(III)complexes(Ir-1 ~ Ir-4)containing 1,2,3-trifluorobenzene and carbazole units in N^N ligands were found,and because of their different triplet excitation,the results showed that Ir-1 and Ir-2 had higher phosphorescence lifetime and higher quantum efficiency than Ir-3 and Ir-4,and can be attributed to different ligand structures.Life can be adjusted by changing the structure and groups of the ligand.To further investigate the relationships of excited-state properties and ligand structures of complexes,DFT calculations have been conducted.Combined with the experimental and theoretical results,we found that the ligand structure is different,the excited state transition form is different.Compared with the triple excited states dominated by 3MLCT transitions,the triple excited states dominated by 3ILCT transitions show longer lifetime of excited states and exhibit better hypoxia detection performance.3.PTMCs usually have very weak luminescence in the aggregated state,that is,aggregation caused phosphorescence quenching(ACPQ),but for some special chemical structure of the PTMCs in the aggregation state not only no luminescence quenching,but light enhancement,that is,aggregation induced phosphorescence emission(AIPE).In order to understand the reason of ACPQ and AIPE and its relationship with the structure of complexes,we have carried on the theoretical research on a series of platinum(II)complexes with AIPE characteristic.Through the study of the structure and excited state properties of ground state and excited state We found that the configuration of the triplet excited state of the platinum(II)complex in the solution was reversed with respect to the configuration in the ground state,and the Schiff base ligand controlled the excited state of the complex,resulting in luminescence in the solution Weak or non-luminescent phenomena.The structural distortions of the platinum(II)complex in the aggregated state lead to the participation of the cyclometallated ligand in the excited state of the platinum(II)complex,resulting in a strong emission in the solid state.