Design And Synthesis Of Blue Fluorescent Emitters Based On Imidazole And Their Electroluminescence Properties

Organic light-emitting diodes?OLEDs?have been widely investigated and commercially tested in recent years and have already been applied in some flat-panel display applications.Nevertheless,there is still much restriction in commercialization for flat-panel displays and general-purpose lightings,one of the factors is the scarcity of efficient emitters with deep blue emission.To promote the application of organic OLEDs in various areas,achieving high performance blue OLEDs with outstanding efficiencies at high luminance and high saturation is still on our wish list.Imidazole,a classical asymmetric aromatic heterocycle,containing two nitrogen atoms with different bonding modes,is endowed with ambipolar nature.Phenanthroimidazole?PI?and pyrenoimidazole?Py I?derivatives are developed to explore the nature of excited states influence on electroluminescence properties.Many OLEDs have been fabricated to optimize the device performance with conventional structure.Futhermore,it is found that doped devices utilizing similar structure of host and guest could display more excellent performance than conventional host-guest system.Our study should provide novel ideas for fabricating highly efficient and stable OLEDs with excellent performance.This work is mainly carred out from the following four aspects:1.Basic photophysical and electrochemical properties of a series of functional materials are characterized to select the proper ones in fabricating blue OLEDs. Injection structures of OLED are optimized and preparation technique of device is improved to get better device performance.2.Two deep-blue molecules,PITO and PISF are desined and synthesized,which share similar chemical structures but exhibit different photophysical and device properties.They consist of phenanthroimidazole and dibenzothiophene analogs with different oxidation states of the S atom.Their doped electroluminescence device are fair-to-middling.We initially find that the doped devices utilizing PITO and PISF as host and guest could display as good performance as conventional host-guest system.3.Some anthracene-and pyrene-functionalized emitters with structure of PI and Py I are choosed to explore their electroluminescence properties.TTA characteristics are found in electroluminescence characteristics.The nondoped OLED of PIMPy exhibits pure blue emission with CIE coordinates of?0.15,0.14?and demonstrates a maximum EQE of 5.11%,stable EQE over 5% at luminance of 300³000 cd m^-2,and a maximum luminance of 54300 cd m^-2.The doped device utilizing PIMPy and Py IPy as host and guest respectively exhibits a maximum luminance over 100000 cd m^-2,maximum EQE of 7.13%,stable EQE over 5% at luminance exceeding 100 cd m^-2.4.A neutral group naphthalene is introduced to 2-position of imidazole in PIM and Py I to to construct efficient deep blue emitters with balanced carriers mobility.Their nondoped OLEDs show negligible efficiency roll-off thaks to the ambipolar nature.Similarly,a doped device is fabricated by dispersing Py INA into PIMNA,a significantly improved EQE of 5.05% is obtained through very effective energy transfer with CIE coordinates of?0.156,0.060?.Besides,the doped device display a quite lagre maximum luminance of 13600 cd m^-2 and relatively low efficiency roll-off with EQE of 4.67% at 1000 cd m^-2,which is among the best of deep blue OLEDs matching the requirement of European Broadcasting Union standard of?0.15,0.06?well.