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Acquiring desirable device performance with deep‐blue color purity that fulfills practical application requirements is still a challenge. Bipolar fluorescent emitters with hybrid local and charge transfer (HLCT) state may serve to address this issue. Herein, by inserting anthracene core in the deep‐blue building blocks, the authors successfully developed two highly twisted D‐π‐A fluorescent emitters, ICz‐An‐PPI and IP‐An‐PPI, featuring different acceptor groups. Both exhibited superb thermal stabilities, high photo luminescent quantum yields and excellent bipolar transport capabilities. The non‐doped OLEDs using ICz‐An‐PPI and IP‐An‐PPI as the emitting layers showed efficient blue emission with an external quantum efficiency (EQEmax) of 4.32 % and 5.41 %, and the CIE coordinates of (0.147, 0.180) and (0.149, 0.150), respectively. In addition, the deep blue doped device based on ICz‐An‐PPI was achieved with an excellent CEmax of 5.83 cd A−1, EQEmax of 4.6 % and the CIE coordinate of (0.148, 0.078), which is extremely close to the National Television Standards Committee (NTSC) standard. Particularly, IP‐An‐PPI‐based doped device had better performance, with an EQEmax of 7.51 % and the CIE coordinate of (0.150, 0.118), which was very impressive among the recently reported deep‐blue OLEDs with the CIEy <0.12. Such high performance may be attributed to the hot exciton HLCT mechanism via T7 to S2. Our work may provide a new approach for designing high‐efficiency deep‐blue materials. [ABSTRACT FROM AUTHOR]

Efficient multifunctional materials acting as violet‐blue emitters, as well as host materials for phosphorescent OLEDs, are crucial but rare due to demand that they should have high first singlet state (S1) energy and first triplet state (T1) 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 T1 into high deep blue emission quantum yield group phenanthroimidazole (PI). As the results, the non‐doped OLEDs based on TPA‐PI‐SBF exhibited excellent EL performance with a maximum external quantum efficiency (EQEmax) 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 EQEmax 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 non‐doped 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 EQEmax of about 20 % and low efficiency roll‐off at the ultra‐high luminance of 10 000 cd m−2. These results provided a new construction strategy for designing high‐performance violet‐blue emitters, as well as efficient host materials for phosphorescent OLEDs. [ABSTRACT FROM AUTHOR]

Two novel bipolar deep‐blue fluorescent emitters, IP‐PPI and IP‐DPPI, featuring different lengths of the phenyl bridge, were designed and synthesized, in which imidazo[1,2‐a]pyridine (IP) and phenanthroimidazole (PI) were proposed as an electron acceptor and an electron donor, respectively. Both of them exhibit outstanding thermal stability and high emission quantum yields. All the devices based on these two materials showed negligible efficiency roll‐off with increasing current density. Impressively, non‐doped organic light‐emitting diodes (OLEDs) based on IP‐PPI and IP‐DPPI exhibited external quantum efficiencies (EQEs) of 4.85 % and 4.74 % with CIE coordinates of (0.153, 0.097) and (0.154, 0.114) at 10000 cd m−2, respectively. In addition, the 40 wt % IP‐PPI doped device maintained a high EQE of 5.23 % with CIE coordinates of (0.154, 0.077) at 10000 cd m−2. The doped device based on 20 wt % IP‐DPPI exhibited a higher deep‐blue electroluminescence (EL) performance with a maximum EQE of up to 6.13 % at CIE of (0.153, 0.078) and maintained an EQE of 5.07 % at 10000 cd m−2. To the best of our knowledge, these performances are among the state‐of‐the art devices with CIEy≤0.08 at a high brightness of 10000 cd m−2. Furthermore, by doping a red phosphorescent dye Ir(MDQ)2 (MDQ=2‐methyldibenzo[f,h]quinoxaline) into the IP‐PPI and IP‐DPPI hosts, high‐performance red phosphorescent OLEDs with EQEs of 20.8 % and 19.1 % were achieved, respectively. This work may provide a new approach for designing highly efficient deep‐blue emitters with negligible roll‐off for OLED applications. [ABSTRACT FROM AUTHOR]

Donor-acceptor (D-A) molecular architecture has been shown to be an effective strategy for obtaining high-performance electroluminescent materials. In this work, two D-A molecules, Ph-BPA-BPI and Py-BPA-BPI, have been synthesized by attaching highly fluorescent phenanthrene or pyrene groups to the C6- and C9-positions of a locally excited-state emitting phenylamine-phenanthroimidazole moiety. Equipped with good physical and hybridized local and charge-transfer properties, both molecules show high performances as blue emitters in nondoped organic light-emitting devices (OLEDs). An OLED using Ph-BPA-BPI as the emitting layer exhibits deep-blue emission with CIE coordinates of (0.15, 0.08), and a maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 4.56 %, 3.60 cd A−1, and 3.66 lm W−1, respectively. On the other hand, a Py-BPA-BPI-based, sky-blue OLED delivers the best results among nondoped OLEDs with CIE y values of < 0.3 reported so far, for which a very low turn-on voltage of 2.15 V, CIE coordinates of (0.17, 0.29), and maximum CE, PE, and EQE values of 10.9 cd A−1, 10.5 lm W−1, and 5.64 %, were achieved, respectively. More importantly, both devices show little or even no efficiency roll-off and high singlet exciton-utilizing efficiencies of 36.2 % for Ph-BPA-BPI and 39.2 % for Py-BPA-BPI. [ABSTRACT FROM AUTHOR]

Abstract: A new blue-emitting carbazole derivative, 3,6-dipyrenyl-9-ethylcarbazole (DPEC), has been designed and synthesized for applications in organic light-emitting devices (OLEDs). Undoped DPEC-based OLEDs give a saturated blue electroluminescence with Commission Internationale de L’Eclairage 1931 coordinates of (0.15, 0.18), and possess high luminous efficiency of 4.75cdA−1. On the other hand, DPEC can also function as a hole-transporting layer (HTL). In particular, by replacing N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) as HTL, a simplified bilayer device demonstrated good performance, comparable to that of the trilayer device. This good device performance illustrates that DPEC is a promising candidate as a blue hole-transporting emitter. [Copyright &y& Elsevier]

Cover Feature: Versatile Host Materials for Highly-Efficient Green, Red Phosphorescent and White Organic Light-Emitting Diodes (ChemElectroChem 23/2019) B The Cover Feature b shows two novel organic deep-blue electroluminescence materials, which could also be used as versatile host materials for highly efficient green, red phosphorescent and white organic light-emitting diodes (OLEDs), simultaneously. Versatile host materials, organic light-emitting diodes, phosphorescence, indolo[3,2,1-jk]carbazole, low roll-off. [Extracted from the article]

High-performance deep-blue emitting phenanthroimidazolederivativeswith a structure of donor–linker–acceptor were designedand synthesized. By using different linkers and different linkingpositions, four deep-blue emitters were obtained and used as emittersor bifunctional hole-transporting emitters in OLEDs. Such devicesshow low turn-on voltages (as low as 2.8 V), high efficiency (2.63cd/A, 2.53 lm/W, 3.08%), little efficiency roll-off at high currentdensities, and stable deep-blue emissions with CIEy< 0.10. Performances are among the best comparing to recentlyreported deep-blue emitting devices with similar structures. The resultssuggest that the combination of the phenanthroimidazole and the donor–linker–acceptorstructure can be an important approach for developing high performancedeep-blue emitters in particular for lighting applications. [ABSTRACT FROM AUTHOR]

Bipolar blue or deep-blue emitting materials are particularly effective to achieve high-performance full color OLEDs. In this study, a novel deep-blue bipolar fluorophore, PPI-F-Cz was designed and synthesized by attaching an electron-withdrawing chromophore phenanthro[9,10-d] imidazole (PI) and an electron-donating group carbazole to the sp3-hybridized C 9 atom of the fluorene. Profiting from balanced carrier mobility, the molecule shows high photoluminescence (PL) and electroluminescence (EL) efficiencies. Using PPI-F-Cz as a non-doped emitting layer (EML), an organic light-emitting device exhibits high performance with CIE color coordinates of (0.155, 0.055), a maximum external quantum efficiency (EQE) of 4.64%, current efficiency (CE) of 7.68 cd/A, and power efficiency (PE) of 8.04 lm/W. Additionally, equipped with the bipolar transport properties and high triplet energy (2.40 eV), PPI-F-Cz was allowed to be used as an efficient host for green and red PhOLEDs with the maximum EQEs of 16.83% and 20.98%, CE max of 58.47 cd/A and 25.19 cd/A, PE max of 53.66 lm/W and 23.28 lm/W respectively. Image 1 • PPI-F-Cz performs well in a multilayer non-doped device (EQE of 4.64% at CIE coordinates of (0.155, 0.055)). • PPI-F-Cz is as an efficient host for green and red PhOLEDs with the maximum EQEs of 16.83% and 20.98%. • All the devices exhibit a low turn-on voltage (<3.0 eV). [ABSTRACT FROM AUTHOR]

Two efficient fluorescence molecules, named 1-(4-trifluoromethylphenyl)-2-(4′-(1,4,5-triphenyl-1H-imidazole-2-yl)-[1,1′-biphenyl]-4-yl)-1H-phenanthro[9,10- d ]imidazole ( PPI-PIM-1 ) and 1-(4-trifluoromethylphenyl)-2-(4′-(2,4,5-triphenyl-1H-imidazole-1-yl)-[1,1′-biphenyl]-4-yl)-1H-phenanthro[9,10- d ]imidazole ( PPI-PIM-2 ) were designed and synthesized, in which the electron-withdrawing trifluoromethyl group was introduced firstly to N1-position benzene of phenanthroimidazole to improve the electron transporting ability and tune the charge transfer (CT) component. In addition, compared to biphenanthroimidazole derivatives, here, we break one rigid plane of phenanthroimidazole to inhibit aggregation-induced-quenching (ACQ) and change the position from C1 to N1 to restrict the conjugation length simultaneously. The devices based on PPI-PIM-1 and PPI-PIM-2 exhibited stable deep-blue emission with CIE coordinates of (0.15, 0.08) and (0.15, 0.07) and achieved maximum external quantum efficiencies of 4.3% and 4.5% respectively. More importantly, the corresponding exciton utilization efficiencies are as high as 27.0% and 30.3%. [ABSTRACT FROM AUTHOR]

By using molecular twisting and bulky side group substitution, we successfully develop two deep-blue emitters, BiPI-1 and BiPI-2 . These two twisted linear molecules retain the excellent photophysical and electrical properties of planar analogue and remarkably supress redshifts in solid state emission. Especially, BiPI-1 showed deep-blue emission in both solution and solid phase, and high carrier mobilities with μ h > 10 −3 cm 2 V −1 s −1 and μ e > 10 −5 cm 2 V −1 s −1 . Standard blue electroluminescence (color purity: (0.15, 0.08)) and high device efficiency (CE: 4.62 cd A −1 , EQE: 6.18%) were observed in a non-doped OLED of BiPI-1 . [ABSTRACT FROM AUTHOR]

Three blue "hot exciton" emitters based on TP-PPI derivatives were constructed for high-performance blue/deep-blue devices and PHOLEDs. [Display omitted] • Materials with high PLQY and excellent thermodynamic stability were synthesized. • Non-doped blue OLEDs were achieved with EQE max of approaching 8%. • Yellow and red PHOLEDs based on o'-PPI-TP showed the best EQE of 26.55 and 20.35%. • Linking position-property relationship between PI and TP unit was unveiled. Here, we designed and synthesized three donor–acceptor (D-A) emitters, 1-phenyl-2-(4-(2-phenyl-[1,2,4]triazolo[1,5- a ]pyridin-6-yl)phenyl)-1 H -phenanthro[9,10- d ]imidazole (m-PPI-TP) , 1-phenyl-2-(4-(2-phenyl-[1,2,4]triazolo[1,5- a ]pyridin-7-yl)phenyl)-1 H -phenanthro[9,10- d ]imidazole (p-PPI-TP) and 1-phenyl-2-(4-(2-phenyl-[1,2,4]triazolo[1,5- a ]pyridin-8-yl)phenyl)-1 H -phenanthro[9,10- d ]imidazole (o'-PPI-TP) , based on [1,2,4]triazolo[1,5- a ]pyridine (TP) as electron-transporting unit and 1,2-diphenyl-1 H -phenanthro[9,10- d ]imidazole (PPI) as hole-transporting moiety serving as emitting block concurrently. All three compounds were demonstrated to be thermally stable with decomposition temperatures (T d) in the range of 454–476 °C and high photoluminescence quantum yields over 86%. Besides, high exciton utilization efficiency (EUE) via "hot exciton" process was proved according to photophysical experiments and theoretical calculations analysis. What's more, the structure–property relationships between different substituted sites of the TP building block and PPI unit were also unveiled. Finally, the non-doped blue and doped deep-blue OLEDs were fabricated with high external quantum efficiency (EQE) approaching 8%. The yellow and red phosphorescent OLEDs (PHOLEDs) based on m-PPI-TP as the host material achieved the best EL performance with EQE of 26.55% and 20.35%, respectively. [ABSTRACT FROM AUTHOR]

Efficient deep-blue fluorescent emitters are of particular significance in organic light-emitting devices (OLEDs). An ambipolar deep-blue emitter, 4,4′-bis(4-(1-(4-( tert -butyl)phenyl)-1 H -phenanthro[9,10- d ]imidazol-2-yl)phenyl)-1,1′-binaphthalene ( 2NBTPI ), was designed, synthesized and applied in a high-efficiency deep-blue emitting OLED. By modifying with binaphthyl, 2NBTPI exhibits a high thermal stability, deep blue emission as well as spatially separated HOMO and LUMO orbits. Comparing with its mononaphthyl counterpart 1,4-bis(4-(1-(4-( tert -butyl)phenyl)-1 H -phenanthro[9,10- d ]imidazol-2-yl)phenyl)naphthalene ( NBTPI ), 2NBTPI shows more balanced charge transport properties, better color purity (color index: (0.15, 0.09) versus (0.15, 0.11)), higher external quantum efficiency (EQE) (5.95% versus 5.73%) and slower efficiency roll-off (EQE roll-off at 100 mA cm −2 : 13.1% versus 27.6%). To the best of our knowledge, OLED performances of 2NBTPI are comparable to the best reported non-doped deep-blue emitters. [ABSTRACT FROM AUTHOR]

Abstract: We report a newly synthesized blue fluorescent pyrene-phenanthroimidazole based emitter Py-BPI and its applications in non-doped organic light-emitting devices (OLEDs). Py-BPI has a high fluorescence quantum yield of 40% and good thermal stability with a high glass transition temperature of 137 °C. Based on Py-BPI, OLEDs with several configurations have been fabricated. Among these devices, an OLED with only two organic layers of Py-BPI and BPhen demonstrates blue emission with high efficiencies of 3.93 cd/A and 3.2 lm/W and maintains a high efficiency of 3.83 cd/A even at a brightness of 5000 cd/m2. Combining with its hole-transporting ability, Py-BPI is shown to be a versatile blue emitter especially suitable for high brightness applications. [Copyright &y& Elsevier]

Charge balance does matter for emission materials to obtain high-performance organic light-emitting diodes (OLEDs), and it is well-known that the electron-transporting ability is inferior to the hole-transporting for the majority of organic emitting materials, especially for blue-emitting compounds. Hence, systematically investigating the effect of the electron-withdrawing group on fluorophore is of vital importance. In this study, we designed and synthesized two deep-blue phenanthro[9,10-d]imidazole (PI) based materials named DPy-PPI and DmPy-PPI by using pyridine-containing groups as electron acceptor as well as adjusting the conjugation length. The photophysical, theoretical, thermal and electrochemical properties of the compounds were investigated systematically, and the relationship between the conjugation length of substituent groups on phenanthroimidazole and the EL performance was clarified. Both of them exhibited good thermal stability and high photoluminescence quantum yields. Non-doped devices based on DPy-PPI and DmPy-PPI as emitter achieved deep-blue emissions with the Commission Internationale de L'Eclairage (CIE) index of (0.14, 0.06) and (0.15, 0.08) and high external quantum efficiencies (EQE max) of 4.24% and 3.74%, respectively. Meanwhile, using DPy-PPI and DmPy-PPI as the host materials, yellow-orange phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated with EQE max , CE max and PE max of 20.55%, 63.86 cd/A, 37.08 lm/W and 18.14%, 55.84 cd/A, 32.47 lm/W, respectively. Furthermore, the red PHOLEDs were also constructed using DPy-PPI and DmPy-PPI as the host with EQE max , CE max and PE max of 14.53%, 17.04 cd/A, 18.51 lm/W and 16.62%, 23.58 cd/A, 21.16 lm/W, respectively. And we believe this work can provide some insight suggestions for scientific researchers to design deep-blue emitting materials. Two deep-blue emitters were constructed by using pyridine group as acceptor. The non-doped device, yellow-orange and red PhOLEDs were fabricated. Image 1 • Non-doped deep blue OLED based on DPy-PPI as emitter was achieved with EQE of 4.24% and CIE coordinates of (0.14, 0.06). • DPy-PPI and DmPy-PPI are the efficient host materials for yellow-orange and red PHOLEDs. • DPy-PPI have more balanced carrier transporting ability than DmPy-PPI. • DPy-PPI and DmPy-PPI have good thermal stability and high photoluminescence quantum yields. [ABSTRACT FROM AUTHOR]