Theoretical Study On Optoelectronic Properties Of Organic Blue Emitting Materials

In this work,two novel blue emitting materials 2,7-bis (N-phenyl-a-naphthylamino)-9,9-diethyl-fluorene(PNAEF)and pyrazolo-[3,4-b]-quinoline derivatives(PAQ)will studied by quantum chemistry methods.The optoelectronic properties from this two materials also will be investigated.By density functional theory(DFT)B3LYP methods,the PNAEF in neutral and cationic states were optimized.The result suggest that,when PNAEF transform HOMO to LUMO,the electronic transmission of PNAEF is mainly the fluorine partâ†'naphthalene part.The calculated ionization energy Ip of PNAEF is 5.71eV,which is as same as the Ip of NPB.The absorption spectrum of PNAEF was calculated,and the maximum absorption peaks were 358.1nm and 257.4nm,which is agree with 360nm and 275nm from experiment.In detail,the corresponding transfer from HOMO to LUMO is main part of this spectra,and from the orbit symmetry,the transfer is pâ†'p~*.The fluorescence efficiency of PNAEF was measured is 0.55,using the 355nm as the exited wavelength and 461nm as the detecting wavelength.By cyclic voltammetry methods,the HOMO(-5.01eV)and LUMO(-2.22eV)energy was measured.The HOMO energy is low,that means the hole inject and transport ability of PNAEF is good.The maximum emission wavelength is at 461nm for device ITO/CuPC/PVK:PNAEF(5%)/ BCP/AlQ3/LiF/Al device and it's CIE was calculated is at(0.153,0.137).This result suggest that PNAEF is a pure blue emission materials for OLED.By density functional theory(DFT)B3LYP methods,the PAQ in ground states were optimized and the molecular structure of PAQ in first singlet excited state was optimized by CIS/6-31+G(D).The calculated results suggest that the fluorescence efficiency of PAQ depends on the intra-molecular charge transfer.The coplanar plane structure benefits the fluorescence efficiency of PAQ.By cyclic voltammetry methods,the HOMO(-5.86eV)and LUMO(-3.03eV) energy of MC1 was measured.The LUMO energy is high,that means MC1 has a good electron transport ability.We fabricated the single layer device for MC1,the maximum emission wavelength is at 489nm as same as its maximum photoluminescence wavelength.This result suggests that the electroluminescence and photoluminescence were from same electronic transmission electron transfer.But the brightness of single layer device is low,which is the quenching results between PAQ and other parts in MC1 molecular.