Design,Synthesis And Photophysical Properties Of Luminescent Zinc(?) Complex Based On Donoracceptor Ligand

Efficient utilization of triplet excitons for luminescent molecular compounds are of critical importance to their applications in the areas of optoelectronic materials and devices,luminescence sensing,photocatalysis/solar energy conversion,bioimaging,and anticounterfeiting and safety.For example,phosphorescent iridium(III)complexes have been successfully used in Organic Light Emitting Diodes(OLEDs)for commercial applications.While,the current triplet emitters are mainly based on noble metal elements such as iridium,platinum,ruthenium,and palladium,all of which are highly expensive and,probably toxic.As alternatives,luminescent zinc(II)complexes held advantages in low cost,mild toxicity,and simple synthesis.However,due to the higher ionization potential of Zn(II)ion,zinc(?)complexes typically have weak spin-orbit coupling in their lowest excited states.As a result,the utilization of their triplet excitons has been a challenging issue,which greatly restrict their practical use.Therefore,exploration of the photophysical property-structure relationship for zinc(?)complexes remains an important topic for the of development of new Zn(II)emitters that are capable of harvesting their triplet excitons.In this thesis,we designed and synthesized two types of luminescent zinc(?)complexes containing newly designed donor-acceptor type ligands.The newly developed Zn(II)complexes have been found to exhibit intriguing photophysical properties including TADF and phosphorescence at room temperature,which have been seldomly reported for Zn(II)complexes.The relationship between their photophysical properties and structures has been discussed,shedding light on the further design of luminescent Zn(II)complexes which may find practical use in OLEDs and related areas.The research results obtained are as follows:1.By choosing pyridine as the acceptor unit(A),phenoxazine and 9,10-Dihydro-9,9-dimethylacridine as the donor(D)group,the donor-acceptor-type(D-A)ligands Ph OPy-PXZ and Ph OPy-DMAC were synthesized.Two penta-coordinated zinc(?)complexes Zn(Ph OPy)-PXZ and Zn(Ph OPy)-DMAC with a dinuclear structure were obtained after coordination.Both Zn(Ph OPy)-PXZ and Zn(Ph OPy)-DMAC show prompt fluorescence and thermally activated delayed fluorescence(TADF)properties with PLQY of up to 50% in solid state,representing one of the highest values ever reported for solid state Zn(II)emitters.The lifetime in the range of 2.09-2.45 ?s for the delayed fluorescence indicate their faster reverse intersystem crossing.The presence of dinuclear core in the molecular are conceived to facilitate the RISC process and maintain a rigid molecular structure in the excited state,both of which are beneficial for efficient TADF.2.A new bidentate donor-acceptor-type ligand,PIM-DMAC,was designed and synthesized by selecting phenanthroimidazole as acceptor and 9,10-Dihydro-9,9-dimethylacridine as donor.Three mononuclear zinc(?)complexes,Zn-PIM-Cl,Zn-PIM-Br,Zn-PIM-I,were obtained using this ligand.Spectroscopic studies reveal that the new Zn(II)complexes exhibit dual emission of fluorescence and phosphorescence in dichloromethane solution,but the powder of zinc(?)complexes show phosphorescence emission only.Further investigation reveals that the dual-emission phenomenon may be caused by the fact that the single molecule can emit both fluorescence and phosphorescence simultaneously.The fact that the powder emits phosphorescence only may be due to the strong self-absorption of the complex,which leads to the quenching of the fluorescence in the short wavelength region.The unique dual fluorescence and phosphorescence emission endow the Zn-PIM-Cl,Zn-PIM-Br,and ZnPIM-I complexes great potent for various applications,such as ratiometric oxygen sensor and single molecule white-lighting emitters.