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Theoretical Study And Structural Design Of The Luminescent Material Tris(8-hydroxyquinolate)aluminum Alq3-nRn(n=0,1) And Its Derivatives

Posted on:2009-02-24Degree:MasterType:Thesis
Country:ChinaCandidate:S H DongFull Text:PDF
GTID:2121360272973111Subject:Materials Physics and Chemistry
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The study of organic electroluminescent material has been paid more and more widely attention recently.Most of researches concerning organic functional material indicate that organic ligand plays an important role in its complex.As significant electron transport material and emitting layer,the luminescent properties of tris-8-hydroxyquinolate-aluminum(Alq3) and its ligand,8-hydroxyquinolate,have been investigated in many works.Recently,Complexes with difluorinated Alq3 and 5-coordinated Alq3 have been paid widely attention in experiment and theory.Just for excited-state formation plays intrinsic role in organic light-emitting diode(OLED) devices,the excited state properties of complexes with difluorinated and 5-coordinated Alq3 may be of greater significance.Some luminescent spectrum of difluorinated and 5-coordinated Alq3 has been measured in experiment.In theory,the geometry structures of complexes with difluorinated and 5-coordinated Alq3 in ground state were optimized with ab initio HF and DFT method.On the basis of the optimized geometry structure,electronic absorption and emission spectrum have been calculated with the time-dependent density functional theory(TD-DFr) and CIS in order to discuss the relation between the electron transition mechanism and the spectrum properties.It is found that the emissions of complexes with difluorinated and 5-coordinated Alq3 originate from the electronicπ→π* transitions within the 8-hydroxyquinoline ligands.That means that one might tune the emission wavelengths and improve charge transfer properties through the effect of substituent on the 8-hydroxyquinoline ligand.The detailed contents of our study are in the followings:(1)Electronic structures and spectroscopic properties of Alq3 and its difluorinated derivatives were studied by the ab initio HF and DFT methods.The ground- and excited-state structures were optimized by the DFT-B3LYP and CIS methods,respectively.The absorption and emission spectra were calculated with TD-DFI" methods based on the ground- and excited-geometries.For difluorinated Alq3,the substituent leads to a decline of the lowest unoccupied molecular orbital (LUMO) energy level of Alq3 and an increase of the electron affinity(EA),which makes the electron carrier injected from the metal electrode easily.As compared to the non-substituted Alq3,the 5,6-difluoro-substituted(2) and the 5,7-difluoro-substituted Alq3(3) give only a slight red-shift influence on the spectra,while the 6,7-difluoro-substituted Alq3(4) shows blue-shift.In view of the electronic reorganization energy(λe),the complexes 2 and 4 are expected to be potential electron injection and transport materials.In addition,the results provide an approach to obtain the important blue luminescence material by strong electron-withdrawing di-substituents at 6,7-positions of phenoxide sides.(2)The structure and electronic properties of 5 and 6-coordinated complexes were investigated theoretically by means of quantum mechanical calculations based on DFT and TD-DFT using the B3LYP functional.Geometry optimizations of the complexes were performed for the ground state (S0) and the lowest exited stated(S1,calculated using CIS method).The second ligand(R2) is found to be important contributors in the geometry structure and the charge transfer properties of the complexes.In addition,the second ligands substitutes also noticeable affect the vertical ionizations (V/P),which will be expected to be used as selective hole-block materials to increase the efficiency and lifetime of the OLED.The nature and the energy of the first singlet-singlet electronic transitions have been obtained from TD-DFT,and radiative lifetimes were calculated as well.As for tuning the spectra properties,it is indicated that the methyl at 4-position of quinoline would be more efficient to get blue light materials,and could obviously affect the radiative lifetimes.
Keywords/Search Tags:difluorinated, 5-coordinated Al complexes, electronic structure, excited state, spectra properties
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