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Synthesis And Electroluminescence Of Organic Blue Fluorescent Materials And Phosphorescent Host Materials

Posted on:2013-09-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:T ZhangFull Text:PDF
GTID:1228330395998962Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
A series of blue organic fluorescent materials and phosphorescent host materials were designed and synthesized. The electroluminescent properties of these materials were studied. The material types and their specific works are as follows:(1) Polyfluorene (PF)-type of blue fluorescent materials:A group of fluorene-based copolymers were synthesized by introduction of different content ratios of electron-withdrawing groups, such as trifiuoromethylphenylene or p-difluorophenylene, to the polymer backbone through Suzuki polycondensation reactions. In contrast to the pristine polyfluorene, these copolymers possess increased fluorescent quantum yields and improved spectra purity and stability of the blue fluorescence. Organic light-emitting diodes were fabricated by spin coating method using them as emitting layer and pure blue electroluminescence was obtained. A maximum external quantum efficiency of1.14%and the CIE (0.16,0.13) were achieved for PF-33F device, which far exceed those of the control device base on the parent polyfluorene.(2) Fluroene-or carbazole-cored small molecular blue fluorescent materials:By introducing9-naphthylanthracene endcaps into oligofluorene or carbazole core through Suzuki coupling reactions, two series of blue fluorescent molecules have been designed and synthesized. These materials exhibit excellent thermal and amorphous stabilities, and high fluorescence quantum yield. Vacumn deposited organic light-emitting devices (OLEDs) using these materials as non-doped emitter exhibited bright deep blue electroluminescence, and the CIE coordinates are quite close to the National Television System Committee (NTSC) standard blue of (0.14,0.08). The devices based on NAECz exhibit excellent device performances with maximum r efficiencies of6.91cd A"1and7.60%, which are among the best performance ever reported for deep-blue OLEDs with a low CIE coordinate y<0.1. In addition, the white OLEDs using NAECz as blue host and a traditional fluorophore DCJTB as yellow dopant realized a high luminance of36250cd m"2and an efficiency of17.75cd A-with an almost standard white light coordinates of (0.35,0.36), which is also among the best results ever reported for two-emitting-component white OLEDs based on fluorescent materials.(3) Small molecular bipolar phosphorescent host material:We report the synthesis and properties of one novel CBP derivative, CBP-CN, with two cyano groups (CN) at the3-sites of both carbazole rings. The strong electron-withdrawing CN was introduced with expectation to promote electron-injecting/-transporting abilities and to achieve bipolar feature for CBP-CN. In comparison with the parent CBP, CBP-CN possesses lowered HOMO and LUMO levels and dramatically increased Tg(162℃), but unaltered HOMO-LUMO band gap and triplet energy (2.69eV). Green and red PhOLEDs were fabricated with CBP-CN as hosts for traditional iridium phosphors. The maximum luminance efficiency (ηL) of80.61cd A-1(23.13%) was achieved for green PhOLED, and10.67cd A-1(15.54%) for red one, respectively, which represent a efficiency increase by25-33%than those of the best devices with CBP host. The efficiencies of the present green PhOLEDs are even close to the best data for phosphorescent OLEDs reported so far (92.2cd A-1and26.8%).(4) Dendritic phosphorescent host materials:A group of dendrimers with oligo-carbazole dendrons appended at4,4’-positions of biphenyl core, namely G1, G2and G3, were synthesized by Ullmann coupling reaction. In comparison with the traditional small molecular phosphorescent host CBP, the dendritic conformation affords these materials with extra merits of being inherent amorphous with extremely high glass transition temperatures of e.g.376℃and being suitable for solution-processing techniques to make devices, in addition to the similarly high triplet energies (2.60-2.62eV). In comparison with the widely-used phosphorescent polymer host polyvinylcarbazole (PVK), these dendrimers possess much higher HOMO levels (-5.51eV to-5.37eV). These dendrimers were used as host materials for iridium phosphors to fabricate OLEDs by spin coating method and excellent performance were achieved. The green and orange PHOLED containing G2host exhibited high luminance efficiencies of38.71cd A-1and32.22cd A-1, respectively, which far exceed those of the control device with PVK host and are among the best results for solution-processed PHOLEDs reported so far.(5) Solution-processible small molecular phosphorescent host materials:A group of small molecular phosphorescent hosts based on a tridurylboranes core and oligofluorene endcaps, namely DBF1DBF2, were synthesized via Suzuki coupling reactions. These materials show good solubility and excellent thermal stability. DBF1has high triplet energy. Green phosphorescent OLEDs were fabricated by partially solution-processing technique with DBF1as host and exhibited good device performances with high efficiencies of36.77cd A-1,23.09lm W-1and10.81%.
Keywords/Search Tags:Organic light-emitting diodes(OLEDs), Blue fluorescent materials, Phosphorescent host materials, Dendrimer, Bipolar
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