Synthesis,Photophysical Properties Of Platinum(Ⅱ) Complexes Based On Pyridine-imidazole Ligands

The strong spin-orbit coupling of the Pt allows for efficient intersystem crossing（ISC）between singlet and triplet states,which can lead to a high quantum yield of emission from the triplet state.Thus,Pt（II）complexes has received widespread attention.Meanwhile,the pyridine-imidazole moiety ways to modifiability and for electron transport ability.In this thesis,four pyridine-imidazole derivatives（L1～L4）and three series of crystals of eleven mononuclear divalent platinum complexes have been synthesized.Testing the luminescence spectrum of the complexes at 293 K and77 K.The main research contents are as follows:1.Four novel pyridoimidazole ligands（L1～L4）by introducing different substituents（-CH₃O,-Cl and-I）.Furthermore,three series of eleven mononuclear Pt（II）complexes were synthesized by using ligands and O^Oβ-diketonato ligand（2,2,6,6-tetramethylheptanedione（dpm）,dibenzoylmethane（dbm）and acetylacetone（Hacac））.The single crystal structure show that the Pt（II）ions at the center of the mononuclear platinum complex all forming typical planar quadrilateral geometry.Crystal structure analysis proves that there is no obvious stacking interaction between molecules,reducing concentration quenching.2.UV-Vis spectra and TD-DFT calculations show that the complex in dichloromethane has ligand-to-ligand charge transfer（L’LCT）,Intra-ligand charge transfer（ILCT）and metal-to-ligand charge transfer transition（MLCT）in the long-wave region（330 nm～430 nm）.Complex also shows good photoluminescence performance in dichloromethane,and the photoluminescence quantum yield（Φ）is greater than 7.8%(of whichΦ_{Pt L3dbm}=29.28%).By changing the substituents on the ligands and auxiliary ligands,green to yellow-green emission（533 nm～546 nm）was achieved.The luminescence lifetime of this kind of complex is 6.56μs～14.65μs at293 K and 13.46μs～17.97μs at low temperature 77 K,showing strong spin-orbit coupling of the Pt complex;It is worth noting that the luminescence wavelength of Pt L3dbm is 546 nm,and the luminous efficiency of 29.28%achieves high-efficiency yellow-green light emission,which is a potential electroluminescent material.The phosphorescence emission of the complex at 77 K proves that the phosphorescence emission of this series of platinum complexes is mainly from the ligand-centered（C^N）character（³LC）and metal-to-ligand charge transfer（MLCT）.