Search

Here, we demonstrate deep-blue carbon dots (CDs) with luminescence centered at 415 nm and PLQY exceeding 60% via nitrogen doping. A bright and high-color-purity CDs-based light-emitting diode (CLED) is achieved with an external quantum efficiency (EQE) of 1.74%, a maximum luminance of 1155.0 cd m−2, and a colour coordinate (0.16, 0.08) closely approaching the HDTV standard color Rec.BT.709 (0.15, 0.06) specification. [ABSTRACT FROM AUTHOR]

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]

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] pyridine (TP) unit at the N1 position of phenanthroimidazole (PI), two luminescent materials, PTPTPA and PTPTPA, were obtained. Systematic photophysical analysis showed that the TP block is suitable for constructing hybridized local and charge‐transfer (HLCT) emitters. Its moderate electron‐withdrawing ability and rigid planar structure can enhance the CT component while ensuring color purity. In addition, compared with PTPTPA, the additional phenyl ring of PTPBPTA not only increased the oscillator strength, but 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. A nondoped device based on PTPTPA as emitter showed impressive performance with EQEmax 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, a white OLED with a high EQE of 23.85 % was achieved. The successful design of PTPTPA not only provided an optimization choice for OLED emitters, but also demonstrated the empirical rules for the design of multifunctional deep‐blue emitters. [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]

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]

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]

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]

A novel near ultraviolet (NUV) emitter, PIBCz, was designed and synthesized by attaching C3-position of the weak electron-donating N-phenylcarbazole group to C6- and C9-positions of phenanthroimidazole (PI) unit for limiting the molecular conjugation and intramolecular charge transfer (ICT) process. The new emitter exhibits strong NUV emission both in solution and thin film as well as good thermal and morphological stability. The PIBCz-based non-doped device shows a perfect color purity of CIE (0.15, 0.05), a very low turn-on voltage of 2.7 V and a maximum external quantum efficiency (EQE), current efficiency (CE) and power efficiency (PE) of 2.74%, 1.28 cd A −1 and 1.12 lm W −1 , respectively, which is comparable to state-of-the-art non-doped OLEDs in similar color gamut. This work demonstrates that effective management of ICT process is a valuable strategy to develop high efficiency NUV emitters. [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]

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]