Synthesis And Optoelectronic Properties Of Bipolar Host Materials Base On Fluorene And Organometallic Phosphorescent Materials

The bipolar host material is one of the most potential host materials for electro-phosphorescent devices. In this thesis, two series of excellent bipolar host materials are designed and synthesized by utilizing 4,5-diazafluorene segment as the backbone structure. These bipolar host materials are also used as ligand for the synthesis of highly luminescent Cu(I) complexes. Their photo-and electro-luminescent properties are systematically studied. We also synthesize two series of sharp red emitting 3d-4f heterodimetallic complexes. The EL device with excellent performance was fabricated based on a heterodimetallic complex.1. Two series of bipolar host materials are designed and synthesized by utilizing 4,5-diazafluorene segment as backbone structure. The compounds are characterized by 1H NMR, MS and elemental analysis. Six single crystals of the compounds were determined by X-ray diffraction. HOMO/LUMO energy levels of the compounds were obtained through electrochemistry analysis and modeling theory. The results indicated that:these kinds of compounds exhibit apparent bipolar properties. The HOMO/LUMO energy levels and carrier transporting ability can be modified by introducing electron-donating moieties into the molecule. Compared with traditional host material CBP, the above compounds have higher triplet energy levels (ET) and more suitable HOMO and LUMO energy levels. The above characteristics can be confirmed by doping Ir(ppy)3 into the host materials and investigating their EL performance. The results illustrated that these compounds are good bipolar host materials for electrophosphorescent devices. Among them, the devices base on DPAPAF, DCPAF and DCSBF as host material showed the excellent EL performance with the maximal luminance of 8246.2 cd/m2,1899.1 cd/m2 and 24123.0 cd/m2, and the current efficiencies of 22.62 cd/A,14.93cd/A and 40.83 cd/A, respectively.2. The bipolar host materials are used as ligand for synthesizing Cu(I) complexes owing to the strong coordination ability of 4,5-diazafluorene derivatives. By synergistic coordination of phosphine ligands, halide ion and host compounds with Cu(I), two kinds of Cu(I) complexes(one is neutral type, another is cationic type) have been synthesized. The complexes are characterized by 1H NMR, MS and elemental analysis. Seven single crystals of the complexes were determined by X-ray diffraction. In cationic type Cu(I) complexes, Cu(I) coordinates with two N atoms and two P atom, forming stable distorted tetrahedral geometry. However, halide ions and its reaction conditions influence the final structure markedly. Photophysical properties of the complexes are systematically studied. The results show that:the luminescence of the Cu(I) complexes are 3MLCT phosphorescent emission in nature. The luminescent properties depend profoundly on the state of Cu(I) complexes. In the solid state and PMMA film, Cu(I) complexes show much more efficient phosphorescence than in solution. Large rigid configurations of the complexes eliminate the possibility of flattening distortion in the excited states and finally enhance the luminescence efficiencies. The tri-coordinated Cu(I) complexes in the solid state exhibit intense photoluminescence because of the slightly distortion in the excited state. The EL properties of Cu(SBF)(PP)(BF4), Cu(DPAPAF)(PP)(BF4), CuI(SBF)(P), Cu(DPASBF)(PEP)(BF4) and Cu(DISBF)(PP)(BF4) are studied. Among the five complexes, Cu(DPASBF)(PEP)(BF4) and Cu(DPAPAF)(PP)(BF4) exhibited better EL properties. The EL device with Cu(DPASBF)(PEP)(BF4) as emitting dopant showed a maximum luminance of 1614.80 cd/m2, a maximum current efficiency of 6.11 cd/A, demonstrating excellent bipolar transporting properties of DPASBF and DPAPAF.3. Two series of d-f heterobimetallic complexes are synthesized by using Shiff base Zn(II) as second ligands and TTA and TFA as the first ligands. The single crystal of complex Eu(TTA)2(TFA)(ZnS2) is obtained and confirmed. The photophysical properties show that:the complex exhibits efficient red emissions typical of Eu3+ion and no emission bands from Shiff base Zn(II) are observed, suggesting that the energy transfer from the Shiff base Zn(II) to the Eu(III) centre is very efficient. We also found that the luminesce efficiency of the salicylaldehyde series complexes is higher than the vanallic series. The higher sensitization efficiency of the salicylaldehyde series complexes maybe the main resaon for this result. The lower triplet energy levels of the vanallic Shiff base Zn(II) ligand and the back energy transfer to the LMCT state may causing the lower luminesce efficiency of the vanallic series. The EL properties of complex Eu(TTA)2(TFA)(ZnS2), with the highest luminesce efficiency among the complexes, is studied. The triplet device base on Eu(TTA)2(TFA)(ZnS2) as emitting dopant showed a maximum luminance as high as 1982.5 cd/m2 and a maximum current efficiency of 9.9 cd/A, corresponding power efficiency of 5.2 lm/W and external quantum efficiency of 5.3%. This result ranks the complex Eu(TTA)2(TFA)(ZnS2) as one of the most efficient europium-based electroluminescent materials.