indexbluehost

IndenocarbazolebasedbipolarhostmaterialsforhighlyefcientyellowphosphorescentorganiclightemittingdiodesGyeongHeonKima,RajuLampandea,ByoungYeopKanga,HyeongWooBaea,JuYoungLeea,JangHyukKwona,*,JungHwanParkb,**aDepartmentofInformationDisplay,KyungHeeUniversity,26,Kyungheedae-ro,Dongdaemun-gu,Seoul,130-701,RepublicofKoreabDuksanNeoluxCo.
,Ltd.
,21-32,Ssukgol-gil,Ipjang-myeon,Seobuk-gu,Cheonan-si,Chungcheongnam-do,331-821,RepublicofKoreaarticleinfoArticlehistory:Received3November2015Receivedinrevisedform29December2015Accepted2January2016Availableonline16January2016Keywords:BipolarhostIndenocarbazolePhosphorescenceOrganiclight-emittingdiodesTripletenergyabstractWereportbipolarhostmaterialswithrobustindenocarbazoleandbiphenylmoietyashole-electron-transportingunitforphosphorescentyelloworganiclight-emittingdiodes(OLEDs).
Newhostmate-rialsdemonstratedanexcellentmorphologicalstabilitywithhighglasstransitiontemperatureof207C.
Simultaneously,italsorevealedappropriatetripletenergyofabout2.
6eVforidealtripletenergytransfertoyellowphosphorescentdopant.
AphosphorescentyellowOLEDwithnewhostICBP1(andICBP2)andconventionalyellowdopantiridium(III)bis(4-(4-t-butylphenyl)thieno[3,2-c]pyridinato-N,C20)acetylacet-onate(Ir(tptpy)2acac)showsalowdrivingvoltageof3.
4(and3.
6V)at1000cd/m2,andmaximumexternalquantumefciencyashighas26.
4%.
SuchefcientperformanceofphosphorescentyellowOLEDsisattributedtoagoodchargebalanceandhighelectrontransportpropertiesofhostmaterials.
2016ElsevierB.
V.
Allrightsreserved.
1.
IntroductionSincethediscoveryoforganicelectroluminescentdevices,severalresearchpapershavebeeninvestigatedforthehighper-formanceofphosphorescentorganiclightemittingdiodes(OLEDs).
Phosphorescentmaterialscanharvestbothsingletandtripletex-citons,whichhelpstoachievetheoretical100%internalquantumefciencyofOLEDdevices.
ThefavorableattributesofOLEDsarelowmanufacturingcost,easyfabricationprocess,exibility,highbrightness,fastresponsetime,wideviewingangleandgoodlife-timeyieldetc.
forthesolidstatelighting[1,2].
Although,severalstudieshavebeenreportedtowardshighlyeffectualhost,procientinterfaciallayersandoptimizedarchitecturesbutstilltheintrinsiclimitsofOLEDuptotheirtheoreticallimithavenotbeenreachedyet[3].
Therefore,furtherscienticeffortsareneededinthedi-rectionofnewmaterialdesignforhostwithsuitabletripletenergy,chargetransportandinjectionlayerstoreachthetheoreticallimitofOLEDperformance.
Phosphorescentyellowandbluehostmaterialsarecrucialcomponentinmoderntwostackstandemwhiteorganiclightemittingdiodesforsolidstatelightingapplications[4].
Addition-ally,phosphorescentyellowmaterialsaregettingimportantcom-ponentstohavehighcolorrenderingindexinmodernpropermultiplepeakwhiteOLEDforlightingapplications[5].
TogetahighperformanceofwhiteOLEDs,efcientphosphorescentyellowhostisequallyimportantduetotheirgreatpotential.
Therefore,todeterminehighquantumefciencyandcurrent/powerefciencyofyellowdevices,developmentofnewhostmaterialscontainingnewholeandelectronmoietieswithsuitablebipolarcharacteristics,largetripletenergyandhighchargecarriermobilityaswellasefcientholeandelectrontransportlayersareneeded.
Anotherperformancedecisivefactoristhechargebalance,whichplaysavitalroleindeterminingtheexternalquantumefciencyandcur-rent/powerefcienciesofOLEDs[6].
Properchargebalancenotonlywidenstherecombinationzoneintheemissivelayer(EML)butalsoleadstoahighperformancewithminimizationoftri-pletetripletannihilation[7].
ToachieveaproperchargebalanceintheEML,bipolarcharacteristicsofhostmaterialsareverycrucialforefcientholeandelectronmovement.
Thestrongbipolarcharac-teristicscanbeattainedbyusingappropriateholeandelectrontransportmoietyinthehostmaterials.
Furthermore,properchargebalanceintheemissivelayercanalsobeachievedbytuningtheenergylevelsofhostanddopantsystem[8].
Thishelpstoreduce*Correspondingauthor.
**Correspondingauthor.
E-mailaddresses:jhkwon@khu.
ac.
kr(J.
H.
Kwon),jhpark@dshm.
co.
kr(J.
H.
Park).
ContentslistsavailableatScienceDirectOrganicElectronicsjournalhomepage:www.
elsevier.
com/locate/orgelhttp://dx.
doi.
org/10.
1016/j.
orgel.
2016.
01.
0041566-1199/2016ElsevierB.
V.
Allrightsreserved.
OrganicElectronics31(2016)11e18thechargetrappingemissionbydopantmoleculesandprovidesacompleteenergytransferfromhosttodopantmolecule.
Overthepastfewyears,verylimitedstudieshavebeenreportedondevelopingnewphosphorescenthostmaterialsforyellowOLEDdevices.
The4,40-bis~9-carbazolyl-2,20-biphenyl(CBP)hasbeenoneofthewidelyusedphosphorescentyellowhostmaterial,whichconsistofrobustcarbazolemoietyandbiphenylgroup[9].
TheCBPhasgoodtripletenergybutshowsarelativelylowglasstransitiontemperature(Tg,62C)value,whichcouldresultsinpoorthermalstabilityofthedevice.
Additionally,italsohasahighLUMOenergyvalue,whichmaydirectlyeffectsontheelectroninjectionprop-ertiesfromtransportlayerandformimproperchargebalanceattheemissivelayer,resultsinaveragedeviceperformance[10].
There-fore,toimprovetheperformanceofOLEDs,narrowbandgaphostmaterialswiththeirgoodchargeinjectionpropertiesfromthechargetransportarerequired.
Recently,Hwangetal.
reportedaphenylcarbazoleandpyrimidinebasedphosphorescenthostma-terialwithabandgapof3.
13eV.
Theyshowedamaximumcurrentefciencyof68.
3cd/AandEQEof22.
3%foryellowOLEDdevice[11].
Similarly,Yangetal.
alsodesignedandsynthesizedaphe-nanthroimidazole/carbazolebasedhybridbipolarhostmaterialsforphosphorescentyellowdevicesandwhichhasabandgapof3.
11eVandhighTgvalueintherangeof113e243C.
TheydemonstratedamaximumEQEandcurrentefciencyof19.
3%and57.
2cd/Aforthe2-(4-(9H-carbazol-9-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazoleand(fbi)2Ir(acac)hostdopantcombination[6].
Inourpreviousreport,wedemonstratedamaximumcurrentefciencyof84.
4cd/AfortheBepp2:iridium(III)bis(4-(4-t-butylphenyl)thieno[3,2-c]pyridinato-N,C20)acetylacetonate(Ir(tptpy)2acac)hostdopantsystem[12].
Recently,wereportedseriesofnewgreenhostmaterialswithindenocarbazoleasholetransportingmoiety,andexhibitedanexcellentOLEDdeviceperformances[7].
Encouragingfromtheseresults,wedevelopedhostmaterialsusinginden-ocarbazolemoietytofurtherenhancetheyellowOLEDperfor-mancesintermsofefciencyandlifetime.
Inthiswork,wemodiedthecarbazolebasedCBPcompoundbyaddingefcientindolocarbozolemoietywithdimethylgroupatinnerandouterpositionofthecompoundtodecreasethebandgapandtoimprovethechargebalancepropertyaswellasthermalstabilityofthenewbipolarhostmaterials.
ThenewcompoundwassuccessfullysynthesizedandusedasahostforphosphorescentyellowOLEDs.
Thephoto-physical,electro-chemicalandthermalcharacteristicsofnewmaterialsweresuccessfullyexaminedbyusingUVevisabsorption,photoluminescence(PL),cyclicvoltam-metry(CV),differentialscanningcalorimetry(DSC)andthermog-ravimetricanalysis(TGA)respectively.
2.
Experimentalsection2.
1.
Synthesis2.
1.
1.
9,9-Dimethyl-2-(2-nitrophenyl)-9H-uorene(1)2-(9,9-dimethyl-9H-uoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane(150g,468.
41mmol),1-bromo-2-nitrobenzene(89.
89g,444.
99mmol),tetrakis(triphenylphosphine)palladium(0)(27.
07g,23.
42mmol)andpotassiumcarbonate(2.
2M,640mL,1405.
24mmol)withtetrahydrofuran(2200mL)andwater(500mL)solventswerereuxedfor4hin5Lroundbottomask.
Theso-lutionwasextractedwithdichloromethane,anddriedoveranhy-drousMgSO4.
Afterremovalofsolventunderreducedpressure,nalresiduewaspuriedbycolumnchromatography(eluentdichloromethane/hexane,1:3)togetthepaleyellowsolidof9,9-dimethyl-2-(2-nitrophenyl)-9H-uorene(yield:147.
7g,84%).
1HNMR(CDCl3,300MHz)d(ppm)7.
88e7.
85(m,1H),7.
79e7.
74(m,2H),7.
66e7.
61(m,1H),7.
55e7.
42(m,3H),7.
39e7.
30(m,4H),7.
37e7.
25(m,6H),1.
51(s,6H).
2.
1.
2.
12,12-Dimethyl-11,12-dihydroindeno[2,1-a]carbazole(2)and11,11-dimethyl-5,11-dihydroindeno[1,2-b]carbazole(3)Amixtureof1(56g,459.
78mmol)andtriphenylphosphine(301.
49g,1149.
44mmol)wasdriedinvacuumandlledwithni-trogengasin5Lroundbottomask.
1,2-Dichlorobenzene(2200mL)wasaddedtodissolvethemixtureandreuxedfor12hinnitrogenatmosphere.
Aftersolventremovalwithdistilla-tion,theresiduewasdividedbycolumnchromatography(eluentCH2Cl2/hexane,1:7)to12,12-dimethyl-11,12-dihydroindeno[2,1-a]carbazoleand11,11-dimethyl-5,11-dihydroindeno[1,2-b]carbazole,respectively.
TworesidueswererecrystallizedwithCH2Cl2/hexaneandobtainedwhitesolidof12,12-dimethyl-11,12-dihydroindeno[2,1-a]carbazoleand11,11-dimethyl-5,11-dihydroindeno[1,2-b]carbazole,respectively(yield:12,12-dimethyl-11,12-dihydroindeno[2,1-a]carbazole42.
5g,11,11-dimethyl-5,11-dihydroindeno[1,2-b]carbazole37.
5g,73%).
1HNMR(CDCl3,300MHz)d(ppm)(12,12-dimethyl-11,12-dihydroindeno[2,1-a]carbazole)8.
14e8.
10(m,3H),7.
85e7.
83(m,1H),7.
71e7.
69(d,J8.
0Hz,1H),7.
55e7.
50(m,2H),7.
48e7.
29(m,4H),1.
73(s,6H)(11,11-dimethyl-5,11-dihydroindeno[1,2-b]carba-zole)8.
11e8.
06(m,2H),7.
75e7.
70(m,1H),7.
67(s,1H),7.
49e7.
44(m,1H),7.
40e7.
32(m,5H),7.
26e7.
22(m,1H),1.
60(s,6H).
13CNMR(CDCl3,500MHz)d(ppm)153.
3,140.
3,140.
1,137.
4,135.
3,134.
2,127.
2,126.
8,125.
7,123.
9,123.
5,122.
2,120.
3,120.
0,119.
8,117.
4,112.
3,110.
7,46.
7,25.
7.
2.
1.
3.
11-(4-bromophenyl)-12,12-dimethyl-11,12-dihydroindeno[2,1-a]carbazole(4)Amixtureof2(30g,105.
87mmol),1-bromo-4-iodobenzene(89.
85g,317.
61mmol),copperpowder(7.
40g,116.
46mmol),po-tassiumcarbonate(14.
63g,105.
87mmol)and18-crown-6(2.
80g,10.
59mmol)wasreuxedfor24hinnitrogenatmospherein2Lroundbottomask.
Afterreaction,theresiduewasdividedbycolumnchromatography(eluentCH2Cl2/hexane,1:3).
AndtheresiduewasrecrystallizedusingCH2Cl2/hexane(yield:31.
5g,68%).
1HNMR(CDCl3,300MHz)d(ppm)8.
19e8.
17(d,J8.
1Hz,1H),8.
13e8.
10(d,J7.
2Hz,1H),7.
96e7.
93(d,J8.
4Hz,1H),7.
80e7.
73(m,3H),7.
43e7.
40(d,J8.
4Hz,1H),7.
37e7.
25(m,6H),6.
81e6.
78(d,J7.
2Hz,1H),1.
19(s,6H).
13CNMR(CDCl3,500MHz)d(ppm)154.
4,144.
44,144.
42,139.
5,139.
3,138.
9,133.
2,133.
0,132.
9,127.
0,126.
9,125.
9,125.
2,123.
8,122.
0,120.
4,119.
7,119.
5,119.
4,113.
2,110.
7,110.
6,48.
0,26.
5.
2.
1.
4.
12,12-Dimethyl-11-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-11,12-dihydroindeno[2,1-a]carbazole(5)Amixtureof4(20.
0g,45.
62mmol),4,4,40,40,5,5,50,50-octa-methyl-2,20-bi(1,3,2-dioxaborolane)(12.
74g,50.
19mmol),[1,10-Bis(diphenylphosphino)ferrocene]dichloropalladium(II)(1.
12g,1.
37mmol)andPotassiumacetate(13.
43g,136.
87mmol)wasdriedandlledwithnitrogengasin1Lroundbottomask.
DMF(230mL)wasaddedtodissolvethemixtureandreuxedfor3hinnitrogenatmosphere.
Afterreaction,thesolutionwasextractedwithethylacetateanddriedoveranhydrousMgSO4.
Thedriedsolutionwasltered.
Andnallythesolutionwaspuriedwithcolumnchromatography(eluentethylacetate/hexane,1:3)andrecrystallizedwithCH2Cl2/hexanetogetwhitesolid(yield:13.
7g,62%).
1HNMR(CDCl3,300MHz)d(ppm)8.
21e8.
19(d,J7.
9Hz,1H),8.
14e8.
11(m,1H),8.
08e8.
05(d,J8.
3Hz,2H),7.
81e7.
76(m,2H),7.
57e7.
54(d,J8.
2Hz,1H),7.
37e7.
25(m,5H),6.
80e6.
78(m,1H),1.
45(s,12H),1.
18(s,6H).
13CNMR(CDCl3,500MHz)d(ppm)154.
6,144.
6,144.
0,139.
6,139.
3,135.
94,135.
91,130.
6,126.
8,126.
7,125.
7,125.
1,123.
7,121.
9,120.
1,119.
5,119.
3,119.
3,112.
9,110.
8,84.
2,48.
0,26.
3,24.
9.
G.
H.
Kimetal.
/OrganicElectronics31(2016)11e1812DownloadEnglishVersion:https://daneshyari.
com/en/article/1267024DownloadPersianVersion:https://daneshyari.
com/article/1267024Daneshyari.
com