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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]

To build up efficient host materials, two novel organic small molecules ICz‐PPI and 2ICz‐PPI were designed and synthesized, in which phenanthro[9,10‐d]imidazole (PI) is proposed as a potential luminophore with high stability, while the indolo[3,2,1‐jk]carbazole (ICz) has a high triplet energy and excellent thermal stability. Both exhibited weak intramolecular charge transfer, high decomposition temperature (Td) and high quantum yield. ICz‐PPI and 2ICz‐PPI can act as the emitting layer in non‐doped organic light‐emitting diodes (OLEDs), which achieved an external quantum efficiency (EQE) of 2.47 and 1.94 % with CIE coordinates of (0.153, 0.121) and (0.161, 0.102), respectively. In addition, the high triplet energy allows them to be used as hosts for phosphorescent OLEDs (PhOLEDs). Accordingly, high performance for green (62.5 cd A−1, 70.9 lm W−1, 17.8 %) and red (25.7 cd A−1, 26.9 lm W−1, 19.4 %) had been achieved from the ICz‐PPI‐based PhOLED. Particularly, the ICz‐PPI‐based red PhOLED showed surprisingly low roll‐off and maintained an EQE of 14.9 % at 10 000 cd m−2. Furthermore, an ICz‐PPI‐based white OLED (WOLED) exhibited warm white light (CIEx,y=(0.427, 0.468)) and high efficiencies with a CEmax of 31.8cd A−1, PEmax of 37.0lm W−1 and EQEmax of 14.4 %. [ABSTRACT FROM AUTHOR]

A new ternary acceptor (A)–donor (D)–acceptor (A) asymmetrically twisted deep‐blue emitting molecule, PPI‐2BI, was synthesized by attaching two electrophilic benzimidazole (BI) units to the C2 and N1 positions of a phenanthroimidazole (PI) donor unit. Profiting from the enhanced D–A electronic coupling, the electron injecting and transporting abilities of the new triangle‐shaped A–D–A molecule are considerably improved and the molecule shows high photoluminescence (PL) and electroluminescence (EL) efficiencies. By using PPI‐2BI as a non‐doped emitting layer (EML), the resulting organic light‐emitting device exhibits emission with color coordinates of (0.158, 0.124) and a maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 4.63 %, 4.98 cd A−1, and 4.82 lm W−1, respectively. Additionally, a simple bilayer device using PPI‐2BI as both the EML and the electron‐transporting layer (ETL) also shows an EQE of 3.81 % with little changes to the color purity. Remarkably, a PPI‐2BI‐based doped device emits efficient near‐ultraviolet EL with color coordinates of (0.154, 0.047) and an EQE of 4.12 %, which is comparable to that of the best reported near‐UV emitting devices. Triangular A–D–A: A new ternary acceptor (A)–donor (D)–acceptor (A) asymmetrically twisted deep‐blue emitting molecule, PPI‐2BI, is synthesized by attaching two electrophilic benzimidazole (BI) units to the C2 and N1 positions of a phenanthroimidazole (PI) donor unit. Profiting from the enhanced D–A electronic coupling, the electron injecting and transporting abilities of the new triangle‐shaped A–D–A molecule are considerably improved and the molecule shows high photoluminescence and electroluminescence efficiencies. [ABSTRACT FROM AUTHOR]

A new triphenylamine-bridged fluoranthene derivative, 4-(7,10-diphenylfluoranthen-8-yl)- N-[4-(7,10-diphenylfluoranthen-8-yl)phenyl]- N-phenylaniline (BDPFPA), with a high glass transition temperature of 220 °C has been synthesized and characterized. BDPFPA is a highly fluorescent and versatile material that can be used as a nondoped green emitter and as a hole transporter. BDPFPA was used in a standard trilayer device as the emitting layer, which showed a low turn-on voltage (<3 V) and a high efficiency of 11.6 cd A−1. The device also shows little efficiency roll-off at high brightness. For example, the efficiency can still be maintained at 11.4 cd A−1 (5.4 lm W−1) at a brightness of 10 000 cd m−2. These results are among the best reported for nondoped fluorescent green organic light-emitting diodes. A simple bilayer device, in which BDPFPA serves as a hole-transporting layer, has a maximum power efficiency of 3.3 lm W−1 and the performance is nearly 40 % higher than that of an N, N′-bis(1-naphthyl)- N, N′- diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)-based standard device. [ABSTRACT FROM AUTHOR]

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]

Abstract Deep blue emitters with good stability, high quantum yield, high triplet energy, and good carrier transporting properties are crucial for full color display and white solid lighting. To solve this, We designed, synthesized and characterized two bipolar deep-blue emitters 2-(4-(9,9′-spirobi[fluoren]-2-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (2-PPI SBF) and 2-(4-(9,9′-spirobi[fluoren]-4-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (4-PPI SBF). Both the materials show good stability, high quantum yield and high triplet energy. Equipped with their bipolar properties, 2-PPI SBF and 4-PPI SBF based non-doped devices show impressive performance with maximum external quantum efficiency (EQE) of 4.78% and 5.29% along with desirable color purity of CIE color coordinates of (0.154, 0.105) and (0.155, 0.058) respectively. Interestingly, the high triplet energy allows them to be used as a host for PhOLEDs. High performance green PhOLEDs based on 4-PPI SBF show the maximum EQE, CE and PE of 16.79%, 64.09 cd/A and 67.92 l m/W respectively. And, high performance red PhOLEDs based on 2-PPI SBF and 4-PPI SBF were also achieved with the maximum EQE of 13.07% and 14.83%, respectively. Furthermore, 4-PPI SBF-based WOLED shows high efficiencies with EQE max of 12.27%, CE max of 27.78 cd/A and PE max of 32.68 l m/W. An efficient white OLED with CIE coordinates of (0.367, 0.305) which is slightly deviated from the values of the theoretical white point (0.33, 0.33) was obtained. Graphical abstract Image 1 Highlights • Two deep-blue bipolar universal materials were designed and synthesized. • Non-doped blue OLED based on 2-PPI-SBF and 4-PPI-SBF achieved EQE up to 4.78% and 5.29%, respectively. • The red PhOLEDs using 4-PPI-SBF as host achieved the maximum EQE of 14.83%. [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]

To increase the fluorescence quantum yield of hybrid local and charge-transfer (HLCT) material, we introduce a symmetric linear D- π -A- π -D structure into molecular design and synthesized a new blue emitter, 2,2'-(2′,3′,5′,6'-tetrafluoro-[1,1':4′,1″-terphenyl]-4,4″-diyl)bis(1-(4-( tert -butyl)phenyl)-1 H -phenanthro[9,10- d ]imidazole) ( 4FBTPI ). Organic light-emitting devices employing 4FBTPI as a dopant emitter show good performances, with CIE (Commission Internationale de l’Enclairage) coordinates of (0.15, 0.09), which is very close to NTSC blue light standard (0.14, 0.08), current efficiencies (CE) of 6.03 cd A −1 , external quantum efficiencies of 6.94%. This performance is comparable to those of recently reported state-of-the-art deep-blue materials with CIE y < 0.10. [ABSTRACT FROM AUTHOR]