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For High Efficiency Organic Light-Emitting Materials: Design, Synthesis and Performances Study

Author: LiuYang
Tutor: TaoXuTang
School: Shandong University
Course: Materials Science
Keywords: Organic Light Emitting Diodes OLED red light blue light Aggregation-induced-emission (AIE) excimer H-shaped cis-vinylene
CLC: TN383.1
Type: PhD thesis
Year: 2008
Downloads: 561
Quote: 2
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Organic Light Emitting DiodesOLEDs)are advantages in that they are self-luminous,high-brightness,wide viewing angle,high contrast,thinness,low power consumption,fast response time and flexiblility and are leading next-generation technologies for electronic displays and lighting.As the key components of OLEDs,the development of organic light-emitting materials limits the practaical use of OLEDs to a great extent.In this sense,to study and explore highly efficient fluorescence materials,especially those strongly emissive in the solid state,would be of great importance in both theory and practice.In the three primary RGB(red,green and blue)emitters,the perforemances of red and blue materials still need to be improved further compared with that of the green emitters.In this thesis,we reported several serials of new light-emitting materials,including a series of AlE(aggregation-induced-emission)fluorenone compounds which bearing unique efficiently emissive excimers,red light AIE materials,parallel H-shaped blue light emitters and an asymmetric phenylenevinylene with cis double bond for pure and efficienct blue OLEDs.Aggregation-induced-emission(ALE)is an amazing property for light emitting materials and has attracted much attention.Here we report a new kind of AIE materials:fluorenone derivates 2,7-dip-tolyl-fluorenone(DTFO)and 2,7-bis(4-(tert-butylthio)phenyl)-fluorenone(DSFO).Strong light emissions with large Stokes shift and long lifetime in the solid state are originated from the formation of excimers.The crystal structure of DSFO shows that,every two molecules are bound together even in the ground state by intermolecular hydrogen bonds and forming a particular dimer,when being excited,the dimer would turn into an excimer without arrangement adjustment and likewise without repulsive interaction when the excimer decays back to the dimer,so,the nonradiative decay pathways exist in common excimers are greatly reduced and thus induce a strongly enhanced luminescence in the solid state.OLED devices employing DTFO as light emitting layers are fabricated and evaluated.Based on this study,a new kind of fluorenone-arylamine derivatives possessing vagarious red-emitting Aggregation Induced-Emission(ALE)characteristics was reported for the first time.On the basis of theoretical calculations and experimental results,the AIE was found originating from the unique dimer(excimer)specifically in the aggregates.In virtue of their nice solid state red fluorescence,non doped red light OLEDs based on these AIE active materials were fabricated.The devices exhibited low turn-on voltages of about 3 V,luminescence of 14135 and 4813 cd m-2,efficiency of 1.40 and 0.35 1m W-1based on the two materials.The results demonstrated that such kind of AIE active materials are promising candidates for non doping red-emission OLEDs applications.For efficient blue emitters,four H-shaped multibranched conjugate molecules were synthesized by facile routes.X-ray crystallography disclosed that an exact parallel "H" shape for each molecule,there was no twist between the two side dipoles of "H".These parallel H-shaped molecules are with quite high fluorescence quantum yields.Highly luminescent blue OLEDs were fabricated based on them,at an operating voltage of 10 V,the device brightness can exceed 10,000 cd m-2.Finally,we reported an asymmetric phenylenevinylene with a cis double bond 2-(4-(p-tolyl)styryl)-1,4-dip-tolylbenzene(cis-TSDTB)and its use as efficient deep blue emitter for organic light-emitting diodes(OLEDs)applications.The crystal structure of cis-TSDTB showed torsion configuration and asymmetric geometry, which make it packing in a reduced intermolecular interaction arrangement.And its single crystals showed excellent fluorescence owing to this unique molecular configuration.Typical OLEDs using cis-TSDTB as non-doped emitters exhibited saturated blue light with the CIE 1931 coordinates of(0.15,0.10),which is quite close to the National Television Standards Committee(NTSC)blue standard.High luminescence efficiency(3.4 cd A-1)and high brightness(9855 cd m-2)have been realized in the device.All of these outstanding results indicated that cis-phenylenevinylene will be a promising candidate as blue light-emitting materials.In summary,in the process of the exploration of highly emissive organic solids, we established a new system of AIE materials,which has been selected as "heart cut" paper by ACS;and the red OLEDs based on the red-emitting AIE materials were considered to be original workswhich will appear in the NPG(Nature Pblication Group)-Asia Materials as the "Highlight";developed a new kind of parallel H-shaped molecules and an asymmetric cis-configured phenylenevinylene with out-standing blue light-emitting properties.

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