Synthesis And Properties Of Iridium Complexes And Polymers Based On Dibenzothiophene Groups

The global energy crisis is imminent,and scientists around the world are driving the development of smart energy-saving devices for display and lighting applications.Organic light emitting diodes(OLEDs)have become the most competitive candidates for the next-generation energy-saving displays.OLED technology is used in commercial displays and has quickly captured the market with excellent performance.In particular,the performance of OLEDs were significantly improved as the application of phosphorescent iridium complexes.In addition to the advantages of lightness,thinness,fast response,and flexible processing of OLEDs,phosphorescent iridium complexes also show high quantum luminous efficiency and emission wavelength can be easily adjusted by modifing the molecular structure.In this paper,we have synthesized three different types of iridium complexes or polymers based on dibenzothiophene,such as :1.A small-molecular phosphorescent iridium complex was incorporated into the host material to obtain a near-white light organic electroluminescent device.2.A solution processed electroluminescent device was obtained by incorporating an alkoxycarbazole group into a phosphorescent iridium complex in which dibenzothiophene as a cyclometallating ligand.3.We synthesized a polymer by a Suzuki coupling reaction using tetrabromodibenzothiophene-S,S-dioxide as the core.The thermal properties,optical performance and device performance with the resulted materials were carefully measured.In chapter two,dibenzothiophene was brominated and oxidized with 2-tri-n-butyltinpyridine to obtain bromodibenzothiophene-S,S-dioxopyridine ring metal ligands.The desired iridium complex(3-Py FSO)2Ir Pic and(2-Py FSO)2Ir Pic were synthesized in a two-step procedure: the first step was Ir Cl3·n H2 O reacted with an excess of cyclometalating ligand to give a chloride-bridged iridium dimmers;the second step was a chloride-cleavage of the iridium dimers with 5 equiv of picolinic acid.The resulted iridium complexes(3-Py FSO)2Ir Pic and(2Py FSO)2Ir Pic were obtained.All compounds had good thermal stability and electrochemical properties.Moreover,in this thesis,(3-Py FSO)2Ir Pic and(2-Py FSO)2Ir Pic were used as yellow-emitting fluorescent materials and TCTA as a blue fluorescent host.A single-doped white organic light-emitting diode(WOLED)was successfully prepared by these materials.The WOLED based on(2-Py FSO)2Ir Pic showed the best performance at a brightness of 2.6 cd m-2.The PE is 4.70 lm/W and the ordinate of CIE is(0.244,0.243).In Chapter 3,several green-emitting iridium dendrimers has been successfully designed and synthesized to form non-doped electroluminescent devices.All the iridium dendrimers display green emission,possess good thermal stability and high photoluminescence quantum yields.As well as,non-doped solution-processable OLEDs were successfully fabricated based on the resulting Ir-1,Ir-2 and Ir-3 as green-emitting phosphors.By increasing the density of carbazole dendrons at the edge of the emissive core,luminescence self-quenching caused by the intermolecular interactions in the solid state can be significantly reduced.The decomposition temperature of Ir-2 was as high as 309 ?.Similarly,based on the synthesized Ir-1,Ir-2 and Ir-3 as green light-emitting phosphorescent complexes,undoped solution-processable OLEDs were successfully manufactured.Ir-3 based OLEDs show the best performance,with a maximum luminous efficiency of 0.24 cd/A and a maximum brightness of 2520 cd m-2.This work will provide new ideas for the development of solution-processable undoped electrophosphorescent devices.In Chapter 4,we designed and synthesized several hyperbranched polymers based on dibenzothiophene-S,S-dioxide(SO)and fluorene groups.Fluorene is an important electroluminescent material in OLEDs.SO is an electron-deficient moiety with electron-withdrawing properties and high photoluminescence quantum yield.The combination of the two compounds is expected to obtain polymers with excellent properties.Hyperbranched polymers have the absorption bands not only for fluorene but also for the iridium complexes in the solution.Moreover,all these polymers display excellent thermal stability.The molecular weight distribution is uniform,and the distribution is narrow,indicating high polymer purity.