Design,Synthesis And Properties Of Iridium Complexes Based On Furo[3,2-c]pyridine

Compare to the traditional fluorescent materials,phosphorescent materials can harness both singlet and triplet excitons to achieve 100%internal quantum efficiency?IQE?theoretically.Among the phosphorescent materials,iridium complex has attracted a great academic and industrial attention to used to fabricate organic light-emitting diode?OLED?,because of its high photoluminescent efficiency and short exciton lifetime.No doubt,developing novel C^N ligand and its corresponding iridium complex is significant to improve the efficiency and lifetime of the device.In this thesis,we have adopted furo[3,2-c]pyridine as the basic buiding block in C^N ligand.With the substituent effect and conjugation effect,the emission of the iridium complexes have been successfully adjusted to cover the whole visible region,and the correspongding blue,green,yellow,red,deep red and white devices achieved the maximum external quantum efficiency at 20.0%,31.8%,30.9%,12.0%,8.5%and 29.1%,with the Commission International De L'Eclairge?CIE?coordinates of?0.25,0.48?,?0.30,0.58?,?0.46,0.53?,?0.66,0.32?,?0.70,0.29?and?0.38,0.46?,respectively.1.Unlike the thieno[3,2-c]pyridine,a novel furo[3,2-c]pyridine based Ir complex,namely?pfupy?₂Ir?acac?,has been developed.By replacing sulfur with oxygen,the LUMO level is upshifted while the HOMO level keeps almost unchanged for the resultant furan-containing?pfupy?₂Ir?acac?.As a consequence,the emissive maximum is blue-shifted from 556 nm of?pthpy?₂Ir?acac?to 538 nm of?pfupy?₂Ir?acac?together with an improved photoluminescence quantum yield of 0.80.The corresponding device based on?pfupy?₂Ir?acac?realizes a record-high external quantum efficiency?EQE?of 30.5%?110.5 cd/A?without any out-coupling technology.Even at a luminance of 1000 and 5000 cd/m²,the EQE still remains at 26.6%?96.4 cd/A?and 25.6%?92.7 cd/A?,respectively.Meanwhile,through the methyl modification,the emission peak of?3,5-diMepfupy?₂Ir?acac?is red-shifted back to 556 nm.The corressponding monochromic device achieved EQE of 30.9%?110.8 cd/A?with CIE coordinate of?0.46,0.53?.The two color white device with 26DCzPPy as host exhibited maximum EQE of 29.1%and power efficiency?PE?of 66.1 lm/W.Benefit from the reduced hole injecting barrier,the white device with TCTA as host got an improved maximum power efficiency of 96.5 lm/W,and even at 1000 cd/m²,the PE still matains at 43.1 lm/W.2.By introducing methoxyl?donating effect?into the 4-and 3-position of phenyl ring in?pfupy?₂Ir?acac?,two Ir complexes,namely?4-MeOpfupy?₂Ir?acac?and?3-MeOpfupy?₂Ir?acac?,have been designed and synthesized.It is found that the position of methoxyl plays an important role on the electrochemical and photophysical properties as well as electrophosphorescent device performance.Compared to the reference complex?pfupy?₂Ir?acac?without any methoxyl?538 nm?,?4-MeOpfupy?₂Ir?acac?with 4-position methoxyl shows a blue-shifted emission peaked at 523 nm originating from the methoxyl-induced enhancement of the LUMO level,whereas?3-MeOpfupy?₂Ir?acac?with 3-position methoxyl shows a red-shifted emission peaked at 602 nm originating from the methoxyl-induced enhancement of the HOMO level.The corresponding PhOLEDs based on?4-MeOpfupy?₂Ir?acac?and?3-MeOpfupy?₂Ir?acac?realize highly efficient green and orange electroluminescence with CIE coordinates of?0.37,0.60?and?0.60,0.40?,revealing a state-of-art EQE as high as 29.5%?100.7 cd/A?and 16.7%?43.9 cd/A?,respectively.On this basis,further introduce the hole transmission activity blocks carbazole and diphenyl amine to replace the methoxy,to obtain?Cz-N3-pfupy?₂Ir?acac?,?Cz-N4-pfupy?₂Ir?acac?,?diPh-N3-pfupy?₂Ir?acac?and?diPh-N4-pfupy?₂Ir?acac?,respectively.When 3-position is substituted,the emission of resulting complex is red-shifted according to the donating effect of the substituent group.Therefore,?Cz-N3-pfupy?₂Ir?acac?and?diPh-N3-pfupy?₂Ir?acac?are peaked at557 nm and 626 nm,respectively.However,the emission of resulting complex is not only on the basis of donating effect but also the conjugation effect of the substituent group.?Cz-N4-pfupy?₂Ir?acac?and?diPh-N4-pfupy?₂Ir?acac?thus emit at 541 nm and 555 nm,respectively.Thecorrespondingdevicesbasedon?Cz-N4-pfupy?₂Ir?acac?,?diPh-N3-pfupy?₂Ir?acac?and?diPh-N4-pfupy?₂Ir?acac?achieve a high EQE of 19.9%,14.6%and26.1%,with CIE coordinate of?0.43,0.54?,?0.61,0.38?and?0.46,0.63?,respectively.?diPh-N4-pfupy?₂Ir?acac?is further used to fabricate a two color white device,realizing the maximum power efficiency of 97.4 lm/W,with CIE coordinate of?0.35,0.43?.And the efficiency keeps 39.0 lm/W even at 1000 cd/m².3.Based on?pfupy?₂Ir?acac?,expland the application of the complex based on furo[3,2-c]pyridine toward blue and deep red region by substituent effect and conjugation effect.Firstly,inport the electron-withdrawing group?fluorine and sp² hybridization nitrogen?to phenyl to tune the emission to 497 nm?dfpfupy?₂Ir?pic?and 477 nm?dfpyfupy?₂Ir?pic?.And then low?-?*energy thienyl and benzo[h]thienyl blocks are also introduced to shift the emission to 590 nm?thfupy?₂Ir?acac?and 641 nm?pthfupy?₂Ir?acac?,respectively.Finally,the phenyl is replaced by fluorene or carbazole in different orientation,the resulting complexes in which the C-3 position of fluorene or C-3,2 positions of carbazole directely ligated to iridium show the emission peaked at582 nm?2-Flfupy?₂Ir?acac?,633 nm?2-Czfupy?₂Ir?acac?and 533 nm?3-Czfupy?₂Ir?acac?,respectively.The devices incorporating?dfpyfupy?₂Ir?pic?,?dfpfupy?₂Ir?pic?,?3-Czfupy?₂Ir?acac?,?thfupy?₂Ir?acac?,?2-Czfupy?₂Ir?acac?and?pthfupy?₂Ir?acac?as emitters exhibite excellent EQE of20.0%,31.8%,21.8%,16.6%,12.0%and 8.5%,with CIE coordinate of?0.25,0.48?,?0.30,0.58?,?0.41,0.58?,?0.62,0.37?,?0.66,0.32?and?0.70,0.29?,respectively.These results manifest the superior performance of the complex based on furo[3,2-c]pyridine in blue and deep red region.4.Adopting the hydrogenation reduction strategy,design and synthesize the green?Ir-G2?and blue?Ir-B1?Ir complexes based on 2,3-dihydrofuro[3,2-c]pyridine.The corresponding ethoxy substituted green?Ir-G1?and blue?Ir-B1?Ir complexes are also synthesized as references.Ir-G2shows higher photoluminance quantum yield?PLQY?and shorter lifetime as compare to Ir-G1.As a result,the device containing Ir-G2 achieved a recorded EQE of 28.0%,sightly higher than Ir-G1,with CIE coordinate of?0.29,0.59?.Inversely,Ir-B2 displays a reduced PLQY and its lifetime is sharply cut down.These variation is caused by the striking enhancement in non-radiative rate,which could be ascribed to the weak interaction between C-H of 3-position in2,3-dihydrofuro[3,2-c]pyridine and F atom of 2-position in phenyl.Because the LUMO is extended to the flexible methylene due to the electrowithdrawing nature of fluorine.Profit from the short lifetime,the device based on Ir-B2 shows gentle“roll-off“,with a bluer coordinate of?0.17,0.29?.