Photoelectrical Properties Of Iridium(?)Complexes With Good Electron Mobility

Organic light-emitting devices?OLEDs?have undergone rapid development since their invention almost three decades ago.Currently,OLEDs have taken quite a place in the mobile display market and also begun expanding their presence to TVs market.The cyclometalated iridium???complexes have attracted great attention because of their tunable emission energy,excellent chemical stability and high photoluminescent efficiency.In this thesis,a series of promising iridium complexes were obtained by modifying the structure of the main ligand or ancillary ligand,aiming to enhance the electron mobility,which would benefit electron transport,broaden the recombination zone,balance the distribution of holes and electrons,leading to excellent electroluminescence?EL?performances.1.Two new heteroleptic Ir???complexes with 2-?3,5-bis?trifluoromethyl?phenyl?pyrimidine?tfmphpm?and 2-?2,6-bis?trifluoromethyl?pyridin-4-yl?pyrimidine?tfmppm?as cyclometalating ligands,2-?5-pyridin-4-yl?-1,3,4-oxadiazol-2-yl)phenol?pop?as the ancillary ligand were synthesized and investigated.Both complexes emit green photoluminescence with high quantum yields?Ir?tfmphpm?2?pop?:?max:501 nm,?PL:87%;Ir?tfmppnm?2?pop?:?max:505 nm,?PL:94%?.The electron mobility values of Ir?tfmphpm?2?pop?and Ir?tfmppm?₂?pop?is 6.05-6.21 × 10-6 cm² V-1s^-1 and 6.67-6.90 × 10-6 cm² V-1 s^-1,respectively,under the electric field from 1040(V cm^-1)^1/2 to 1300(V cm^-1)^1/2.To evaluate the EL performances of the two complexes,single emitting layer?EML?devices named G1 and G2 using Ir?tfmphpm?2?pop?and Ir?tfmppm?₂?pop?as the emitters,respectively,were fabricated.The device using Ir?tfmppm?₂?pop?as the emitter shows better EL performances with a maximum luminance?Lmax?,a maximum current efficiency??c.max?,a maximum power efficiency??p,max?and a maximum external quantum efficiency?EQEmax?up to 48 981 cd m-2,92.79 cd A^-1,39.46 lm W^-1 and 31.8%,respectively.Compared the difference between the structures of both emitters,the introducing of one more nitrogen heterocycle to the cyclometalating ligand does effect the nature of Ir?tfmppm?₂?pop?.The better electron mobility and lower LUMO level of Ir?tfmppm?₂?pop?would facilitate the injection and transport of electrons,which would broaden the recombination zone,balance the distribution of holes and electrons,resulting in excellent EL performances,consistent with the design intention.2.Four new green heteroleptic Ir???complexes using 2-?2,6-bis?trifluoromethyl?pyridin-4-yl?pyrimidine?tfmppm?,2-?2,6-bis?trifluoromethyl?pyridin-4-yl?-5-fluoropyrimidine?f-4-tfmppm?and 2-?2,6-bis?trifluoromethyl?pyridin-3-yl?-5-fluoropyrnmidine?f-3-tfmppm?as main ligands and acetylacetonate?acac?or tetraphenylimidodiphosphinate?tpip?as ancillary ligands,with high quantum yields?Ir?tfmppm?₂?acac?:?max:495 nm,?PL:85%;Ir?tfmppm?₂?tpip?:?max:501 nm,?PL:89%;Ir?f-4-tfmppm?2?tpip?:?max:497 nm,?PL:92%;Ir?f-3-tfmppm?2?tpip?:?max:500 nm,?PL:94%?,were synthesized.By decorating the structures of four complexes,the quantum efficiency and the electron mobility were enhanced and the LUMO levels were reduced gradually.The electron mobility values of Ir?tfmppm?₂?acac?,Ir?tfmppm?₂?tpip?,Ir?f-4-tfmppm?2?tpip?and Ir?f-3-tfmppm?2?tpip?are 4.99-5.04 × 10-6 cm² V-1 S-1?5.00-5.45 × 10-6 cm² V-1 s^-1?5.26-5.81 × 10-6 cm² V-1 s^-1 and 6.23-6.92 × 10-6 cm² V-1 s^-1,respectively,under the electric field from 1040(V cm^-1)^1/2 to 1300(V cm^-1)/2.The single EML based on the complexes with tpip as ancillary ligand show better performances than that of the device using the complex with acac as ancillary ligand.Moreover,the introducing of one more F atom and the different positions of substituents also can affect their device performances.And the device based on Ir?f-3-tfmppm?2?tpip?shows the best EL performances with a Lmax,a?c.max,a?p,max and an EQEmax up to 44446 cd m-2,92.83 cd A^-1,76.80 Im W^-1 and 29.5%,respectively.3.Two orange-red Ir???complexes with 1-?2,6-bis?trifluoromethyl?pyridin-4-yl?isoquinoline?tfmpiq?and 4-?2,6-bis?trifluoromethyl?pyridin-4-yl?quinazoline?tfmpqz?main ligands,acac as the ancilary ligand were applied in OLEDs and the devices based on both complexes were investigated.Both complexes Ir?tfmpiq?2?acac?and Ir?tfmpqz?2?acac?,with the strongest emissions peak at 587 and 588 nm,show high quantum efficiency as 0.42 and 0.91,respectively.The introducing of quinazoline,which has the influence on the electric cloud distribution of the complexes,does reduce the LOMO level,enhance the quantum yield and the electron mobility of Ir?tfmpqz?2?acac?greatly.The electron mobility values of Ir?tfmpiq?2?acac?and Ir?tfmpqz?2?acac?are 8.57-8.65 × 10-6 cm² V-1s^-1 and 9.47-10.23 × 10-6 cm² V-1 s^-1,respectively,under the electric field from 1040(V cm^-1)^1/2 to 1300(V cm^-1)^1/2.We researched the single EML devices G1 and G2 using Ir?tfmpiq?2?acac?and Ir?tfmpqz?2?acac?as emitters,respectively.The device G2 exhibits much better performances with a Lmax of 66 716 cd m 2,a ?c,max of 43.76 cd A^-1,an EQEmax of 14.8%,and a ?p,max of 38.17 lm W^-1.The double-EMLs device could achieve better performances than the single-EMLs device because a better balance of carries and a wider recombination zone within EMLs could be realized by the double-EMLs device.Thus,we researched the double-EML devices G3 and G4 using Ir?tfmpiq?2?acac?and Ir?tfmpqz?2?acac?emitters,respectively.Compared with the single-EML devices,both double-EML devices displayed better EL performances and lower efficiency roll-off.The device G4 exhibited much better performances with a Lmax of 96 609 cd m-2,a ?c,max of 59.09 cd A^-1,an EQEmax of 20.2%,and a ?p,max of 53.61 Im W^-1.4.The Ir???complexes based on tfmpiq and tfmpqz display good electroluminescence performances.The introducing of tpip would lead to a better balance of carries due to their four bulky aromatic groups,leading to an increase of the spatial separation from neighboring molecules to suppress triplet-triplet annihilation and triplet-polaron annihilation effectively,as well as the ability of Ph2P=O to improve the ability of electron injection and transportation.The Ir???complexes Ir?tfmpiq?2?tpip?and Ir?tfmpqz?2?tpip?with the strongest emissions peak at 591 and 588 nm,and high quantum efficiency as 0.47 and 0.98,respectively,were applied in OLEDs.The electron mobility values of Ir?tfmpiq?2?tpip?and Ir?tfmpqz?2?tpip?are 6.44-7.20 × 10-6 cm² V-1 s^-1 and 8.93-9.47 × 10-6 cm² V-1s^-1,respectively,under the electric field from 1040(V cm^-1)^1/2 to 1300(V cm^-1)^1/2.The single EML devices and the double-EMLs devices using Ir?tfmpiq?2?tpip?and Ir?tfmpqz?2?tpip?as emitters were studied,respectively.The double-EMLs device based on Ir?tfmpqz?2?tpip?exhibited the best performances with a Lmax of 125 572 cd m-2,a ?c,max of 57.19 cd A^-1,an EQEmax of 18.7%,and a ?p,max of 42.76 lm W^-1.Because the device based on Ir?tfmpqz?2?tpip?showed high efficiency,further work was done to increase its performances.A wide band gap trivalent europium complex Eu?DBM?3phen?DBM = dibenzoylmethide,phen = 1,10-phenanthroline?was selected as a sensitizer codoped into the electron dominant EML of the double-EMLs devices because that Eu?DBM?3phen can function as electron trappers due to its low-lying energy levels,which are helpful in balancing holes and electrons and in broadening recombination zone.What's more,the matched triplet energy of Eu?DBM?3phen is instrumental in facilitating energy transfer from host to emitter.The device G5 displayed better performances with a Lmax,a ?c,max,a ?p,max and an EQEmax up to 129 466 cd m-2,62.96 cd A^-1,53.43 lm W^-1 and 20.2%.5.Aiming to get yellow emitters and devices with high efficiency by improving the electron mobility,two complexes Ir?tfmphiq?2?tpip??tfmphiq = 1-?3,5-bis?trifluoromethyl?phenyl?isoquinoline?and Ir?tfmphqz?2?tpip??tfmphqz = 4-?3,5?bis?trifluoromethyl?phenyl?quinazoline?,with high quantum yields?Ir?tfmphiq?2?tpip?:A.?max:581 nm,?PL:61%;Ir?tfmphqz?2?tpip?:?max:566 nm,?PL:97%?,were synthesized.The electron mobility values of Ir?tfmphiq?2?tpip?and Ir?tfmphqz?2?tpip?are 8.14-8.61 × 10-6 cm² V-1 s^-1 and 9.38-10.00 × 10-6 cm² V-1 s^-1,respectively,under the electric field from 1040(V cm^-1)^1/2 to 1300(V cm^-1)^1/2.The single EML devices were fabricated using Ir?tfmphiq?2?tpip?and Ir?tfmphqz?2?tpip?as emitters,respectively.The device based on Ir?tfmphqz?2?tpip?exhibits much better performances with a Lmax of 96 377 cd m 2,a ?c,max of 106.66 cd A^-1,an EQEmax of 29.7%,and a ?p,max of 64.72 lm W^-1.