Synthesis And Properties Studies Of Star-shaped Blue Emission Molecules Based On 1,3,5-triazine Derivatives

Organic light-emitting diodes（OLEDs）have attracted much more attentions due to their simple preparation,low cost and turn-on voltage,high efficiency and light weight.Over the past three decades,organic electroluminescent materials and OLEDs therefore have gained much progress.However,blue emissive materials still lag behind red and green emissive materials,especially the poor stability and low efficiency for the blue emitter-based devices.In order to further study the structure-property relationship of blue OLEDs,in this dissertation,three D-π-A and four D-A blue organic luminescent molecules were designed and synthesized.The structures of these molecules were characterized by1H-NMR,13 C NMR and TOF-MS.The photophysical properties,electrochemical and thermal properties were evaluated via UV-vis absorption spectra,photoluminescent spectra,cyclic voltammetry and thermal analysisThe main contents of this dissertation are listed as follows:1.Three blue emission molecules named p-TFTPA,mp-TFTPA and m-TFTPA based on 1,3,5-triazine with the donor-bridge-acceptor（D-π-A）structure were designed and prepared.We studied the effect of the changed interconnection position（donor/acceptor/linker）on the photophysical property of these dyes.The research results demonstrated that all of these compounds exhibited good thermal stability.Strong intramolecular charge transfer（ICT）absorption band were observed between250-450 nm（from the donor unit to the accept unit）.Their PL spectra showed the maximum emission peaks in the range of 406⁴74 nm in dichloromethane solution.In addition,the luminescent lifetimes for all compounds were in the nanosecond regime,implying the emission originated from fluorescence.Furthermore,these compounds were employed as emissive dopants in organic light-emitting diodes,and the devices achieved the bluenish-green emission with the highest luminance of 10150cd·m^-2,the highest external quantum efficiency of 2.3% and the maximum current density of cd A-1.2.To enhance the emission efficiency of blue emitter in solid state,we introduce the aggregation-induced emission（AIE）into the D-A molecules.Based on the previous work,herein,four D-A blue emission molecules based on 1,3,5-triazine named pTPA,m-TPA,p-TPA-TPE and m-TPA-TPE were designed and prepared,and their structures were characterized.The effect of AIE unit on the photophysical property were investigated in detail.All compounds exhibited good thermal stability with thedecomposition temperature above 350 oC（5 wt%）.The UV-vis absorption spectra have a strong absorption between 250-500 nm.The PL spectra showed the maximum emission peaks at 454 nm,458 nm,443 nm and 485 nm in toluene solution,respectively.As expected,p-TPA-TPE and m-TPA-TPE presented a strong AIE phenomenon in THF/H₂O mixture.Intense emission with the luminescent quantum yield of 60% and 24% were obtained for p-TPA-TPE and m-TPA-TPE in the neat film,which means that integrating the AIE unit into blue emitter has a clearly positive role for enhancing the emission efficiency.Therefore,we chosed m-TPA and m-TPATPE as the dopant to fabricate both doped and nondoped devices,and their electroluminescent properties were studied preliminarily.The non-doped devices showed a satisfied bluenish-gree emission with the maximum luminance of 3629 cd·m^-2,the maximum current density of 4.2 cd A-1 and the highest EQE of 1.8 %.