Twon ovel bipolar deep-bluef luorescent emitters, IP-PPI and IP-DPPI, featuring different lengths of the phenyl bridge,w ere designed and synthesized, in which imidazo[1,2-a]pyridine (IP) andp henanthroimidazole (PI) were proposed as an electron acceptor and an electron donor,r espectively.Both of them exhibit outstanding thermal stability and high emission quantumy ields. All the devices based on these two materials showedn egligible efficiency roll-off with increasing current density.I mpressively,n on-doped organic light-emitting diodes (OLEDs) based on IP-PPI and IP-DPPI exhibited externalq uantum efficiencies(EQEs) of 4.85 %a nd 4.74 %w ith CIE coordinates of (0.153, 0.097) and (0.154, 0.114) at 10000cdm À2 ,r espectively.I na ddition, the 40 wt % IP-PPI doped device maintained ah igh EQE of 5.23 %w ith CIE coordinates of (0.154, 0.077) at 10000 cd m À2 .T he doped deviceb ased on 20 wt %I P-DPPIe xhibited ah igher deepblue electroluminescence (EL) performance with am aximum EQE of up to 6.13 %a tC IE of (0.153,0 .078) and maintained an EQE of 5.07 %a t1 0000 cd m À2 .T ot he best of our knowledge,t hese performances are among the state-of-thea rt devices with CIE y 0.08 at ah igh brightness of 10000cdm À2. Furthermore, by doping ar ed phosphorescent dye Ir(MDQ) 2 (MDQ = 2-methyldibenzo[f,h]quinoxaline) into the IP-PPI and IP-DPPI hosts, high-performance red phosphorescentO LEDs with EQEs of 20.8 %a nd 19.1 %w ere achieved, respectively. This work may provide an ew approach for designinghighly efficient deep-blue emitters with negligible roll-off for OLED applications.
In this work, four phenanthroimidazole (PI) based isomers TPA-PPI-PBI, TPA-PPI-NPBI, PBI-PPI-TPA and NPBI-PPI-TPA for high-efficiency deep-blue organic light-emitting diodes (OLEDs) have been designed and synthesized.
High-performance deep-blue emitters with external quantum efficiencies (EQEs) exceeding 5% are still scarce in organic light-emitting diodes (OLEDs). In this work, by introducing a [ 1,2,4]triazolo [1,5-a]p yridine (TP) unit at the N1 position of phenanthroimidazole (PI), two luminescentm aterials, PTPTPA and PTPTPA,w ere obtained. Systematic photophysical analysis showed that the TP block is suitable for constructingh ybridized local and charge-transfer( HLCT) emitters. Its moderate electron-withdrawing ability and rigid planar structure can enhancet he CT component while ensuring color purity.I na ddition, compared with PTPTPA,t he additional phenyl ring of PTPBPTAn ot only increased the oscillator strength,b ut also decreased the Stokes shift. TDDFT calculations pointed out facile reverse intersystem crossing processes in PTPTPA from high-lying triplet states to the singlet excited state. An ondoped device based on PTPTPA as emitter showed impressive performance with EQE max of 7.11% and CIE coordinates of (0.15, 0.09). At the same time, it was also an efficient host for yellow and red phosphorescent OLEDs. By doping yellow (PPYBA) and red (BTPG) phosphorescent dyes into PTPTPA,awhite OLED with ah igh EQE of 23.85 %w as achieved. The successful design of PTPTPA not only provideda no ptimization choice for OLED emitters, but also demonstrated thee mpirical rules for the design of multifunctional deep-blue emitters.
Efficient multifunctional materials acting as violetblue emitters, as well as host materials for phosphorescent OLEDs, are crucial but rare due to demand that they should have high first singlet state (S 1 ) energy and first triplet state (T 1 ) energy simultaneously. In this study, two new violet-blue bipolar fluorophores, TPA-PI-SBF and SBF-PI-SBF, were designed and synthesized by introducing the hole transporting moiety triphenylamine (TPA) and spirobifluorene (SBF) unit that has high T 1 into high deep blue emission quantum yield group phenanthroimidazole (PI). As the results, the nondoped OLEDs based on TPA-PI-SBF exhibited excellent EL performance with a maximum external quantum efficiency (EQE max ) of 6.76 % and a violet-blue emission with Commission Internationale de L'Eclairage (CIE) of (0.152, 0.059). The device based on SBF-PI-SBF displayed EQE max of 6.19 % with CIE of (0.159, 0.049), which nearly matches the CIE coordinates of the violet-blue emitters standard of (0.131, 0.046). These EL performances are comparable to the best reported nondoped deep or violet-blue emissive OLEDs with CIEy < 0.06 in recent years. Additionally, the green, yellow and red phosphorescent OLEDs with TPA-PI-SBF and SBF-PI-SBF as host materials achieved a high EQE max of about 20 % and low efficiency roll-off at the ultra-high luminance of 10 000 cd m À 2 . These results provided a new construction strategy for designing high-performance violet-blue emitters, as well as efficient host materials for phosphorescent OLEDs.
Of paramount significance in phosphorescent organic light‐emitting diodes (PHOLEDs) are the facts that Förster resonance energy transfer (FRET) must be sufficient and back energy transfer should be prohibited. Herein, the FRET efficiencies for high‐performance PHOLEDs based on a simple bipolar luminogen 1‐phenyl‐2‐(5′‐phenyl‐[1,1′:3′,1″‐terphenyl]‐4‐yl)‐1H‐phenanthro[9,10‐d]imidazole (PHT‐PPI) with high triplet energy of 2.44 eV are systematically investigated. As a result, with PO‐01 as dopant, the high‐performance orange PHOLED is achieved with maximum external quantum efficiency (EQEmax) of 26.14% and ultrahigh brightness of 152 000 cd m−2, which are the highest reported efficiencies for orange OLEDs with such high brightness. In addition, the green and red PHOLEDs are also fabricated with EQEmax of 15.38% and 16.12%, respectively. Furthermore, the nondoped device based on PHT‐PPI as a deep‐blue emitter is also obtained with an EQEmax of 5.12% and the Commission Internationale de L’Eclairage (CIE) index of (0.15, 0.08). More importantly, the blue, green, orange, and red devices exhibit low efficiency roll‐off, particularly, of which the orange PHOLED is extremely small (<9%) even at the brightness of 10 000 cd m−2.
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