Synthesis And Performance Research Of Pyridazine-based Three-ring Metal Iridium Complexes

In recent years,organic light-emitting diodes?OLEDs?has attracted much attention.As the phosphorescence quenching caused by the interaction between the molecules will reduce the devices'efficiency seriously,many researchers devote themselves into finding ways to prevent phosphorescence quenching.The following ways were reported:doping complexes into host materials?connecting complexes to polymers through covalent bonds?introducing dendritic structures.However,there are lots of disadvantages,like phase separation in mixed systems,randomness of polymer structures,and distortion of oversize volume in dendrimers'structures.Although the emissive cores can be protected well by the dendrimers,synthetic processes of them are complicated.Steric hindrance groups with big space structures can also be used to prevent intermolecular interaction to reduce phosphorescence quenching,and the synthetic routes are simple.In this paper,firstly,by introducing different kinds of steric hindrance groups,the pyridazine-based ligands were produced.Then,we produced pyridazine-based complexes?Dcf3?Dpa?Fen?Tme?in only one step.This is a new way which palys a key role in guiding later workers to get the stable three-ring complexes through a simple way.We pured the ligands into IrCl₃.3H₂O?H₂O and 2-methoxyethanol mixed liquid and refluxed 12 h to produce three-ring iridium complexes:dPhamine?fen?tMe.In addition,tMe was also produced by refluxing the decalin liquid with LTme and IrCl₃.?tht?₃,as there was no water in this system so that compounds dissolved well and the productivity was improved.More importantly,Dcf3 could be got only in the later way.The 3-?trifluoromethyl?phenyl is contained by all the pyridazine-based complexes,it's shape just like a umbrella so that the emissive cores can be protected completely.In addition,steric hindrance groups which different from 3-?trifluoromethyl?phenyl were also introduced to protect emissive cores better.As the HOMO?LUMO levels were influenced by different substituent groups,the pyridazine-based complexes'emissive wavelength were changed.Therefore,complexes with different colours can be produced by introducing different substituent groups with different push-pull electronic performances.Ultraviolet absorption spectroscopy?fluorescence photoluminescence spectra?fluorescence excitation spectra and cyclic voltammetric curves of pyridazine-based complexes were tested.Due to the similar structure,the same spectral characteristics were observed.However,as the steric hindrance groups caused varying degrees of conjugate,complexes showed different HOMO?LUMO levels and energy gaps?Eg?.The Eg of dCF3?dPhamine?fen?tMe is 2.09 eV?2.15 eV?2.28 eV?2.34 eV and the light wavelength of them is 558 nm?533 nm?527 nm?502.5 nm respectively,all of them belongs to green areas.More importantly,the 533 nm of dPhamine is very close to 535 nm?the pure green colour can be seen in this wavelength?,so the dPhamine can be used to fabricate white organic light-emitting diodes?WOLEDs?.Secondly,as containing a alkyl structure which can also be used to protecte emissive cores,the hindered pyridazine-based complexes Mar?Mpcf3?Mmcf3 was produced.The photophysical property of phosphorescent complexes were also tested.We learned that these complexes'emissive wavelength are 526.5 nm?525 nm?509.5 nm,and the 509.5 nm is very close to classic green material Ir?ppy?₃ used to fabricate a collection of efficient devices.So the Ir?ppy?₃ would be replaced by Mmcf3 in some cases.Moreover,with the device structure of ITO/MoO₃?1nm?/Mcp?40 nm?mCP:comples/Bphen?40 nm?/LiF?1 nm?/Al,Mmcf3 was doped into host material mCP in different concertrations and fabricated into a series of devices.The best doping concertration is 20%,the turn-on voltage is 2.6 V,the maximum luminance is 35630 cd/m²?7.5 V?and the maximum current efficiency is 56.74 cd/A,the maximum external quantum efficiency is20.45%,the efficiency is close to the theoretical value.In addition,the nondoped device was also fabricated,the turn-on voltage is 2.4 V,the maximum luminance is 14970 cd/m²?6.5 V?and the maximum current efficiency is 21.62 cd/A,the maximum external quantum efficiency is 9.56%.All devices show very high efficiency which decrease slowly.In conclusion,the complexes introduced in this study are suitable for the preparation of efficient devices.