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Upon fusing the pyrazinyl pyrazole entity in giving pyrazolo[3,4‐f]quinoxaline chelate, the corresponding Os(II) based NIR emitter exhibited "invisible" and efficient electroluminescence with a peak maximum at 811 nm. A maximum external quantum efficiency of 0.97 % and a suppressed efficiency roll‐off till a current density of 300 mA cm−2 was also exhibited. [ABSTRACT FROM AUTHOR]

Near‐infrared organic light‐emitting diodes (NIR OLEDs) enable many unique applications ranging from night‐vision displays and photodynamic therapies. However, the development of efficient NIR OLEDs with a low efficiency roll‐off is still challenging. Here, a series of new heteroleptic Pt(II) complexes (1–4) flanked by both pyridyl pyrimidinate and functional azolate chelates are synthesized. The reduced ππ* energy gap of the pyridyl pyrimidinate chelate, and strong intermolecular interaction and high crystallinity in vacuum‐deposited thin films engender strong intermolecular charge transfer transition including metal–metal‐to‐ligand charge transfer; thereby, exhibiting efficient photoluminescence within 776–832 nm and short radiative lifetimes of 0.52–0.79 µs. Consequently, nondoped NIR‐emitting OLEDs based on these Pt(II) complexes are fabricated, to which Pt(II) complexes 2 and 4 give record high maximum external quantum efficiency of 10.61% at 794 nm and 9.58% at 803 nm, respectively. Moreover, low efficiency roll‐off is also observed, among which the device efficiencies of 2 and 4 are at least four times higher than that of the best NIR‐emitting OLEDs recorded at current density of 100 mA cm−2. [ABSTRACT FROM AUTHOR]

The design of square‐planar Pt(II) complexes with highly efficient solid‐state near infrared (NIR) luminescence for electroluminescence is attractive but challenging. This study presents the fine‐turning of excited‐state properties and application of a series of isoquinolinyl pyrazolate Pt(II) complexes that are modulated by steric demanding substituents. It reveals that the bulky substituents do not always disfavor metallophilic Pt···Pt interactions. Instead, π–π stacking among chelates, which are fine‐tuned by the associated substituents, also exerts strong influence to the metal‐metal‐to‐ligand charge transfer (MMLCT) transition character. Theoretical calculations indicate that Pt···Pt contacts become more relevant in the trimers rather than the dimers, especially in their T1 states, associated with a change from mixed 3LC/3MLCT transition in the monomer/dimer to mixed 3LC/3MMLCT transition character in the trimer. Electroluminescence devices affording intense deep‐red/NIR emission (near 670 nm) with unprecedentedly high external quantum efficiency over 30% are demonstrated. This work provides deep insights into formation MMLCT transition of square‐planar Pt(II) complexes and efficient molecular design for deep‐red/NIR electroluminescence. [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 novel host material featuring a spiro-annulated benzimidazole configuration is exploited for blue phosphorescent organic light-emitting devices (PhOLEDs). The new material exhibits a high triplet energy (3.07 eV) and a bipolar characteristic and is effective as the host for FIrpic-, FIr6- and FK306-based blue PhOLEDs with high performances. [ABSTRACT FROM AUTHOR]

While exciplex formation is considered to have a negative impact on the performance of organic light-emitting devices (OLEDs), it can be utilized as a simple means for manipulating the emission colors. Here, we explore various important factors influencing the exciplex formation in order to provide a simple way for tailoring the emission color of OLEDs involving exciplex emission. In addition to the well-known effects of the energy difference between electron affinity and ionization potential (IP) of organic materials used, we found that electron mobility and IP of electron-transporting layer (ETL) are also critical factors in controlling the intensity of exciplex emission via the influence on charge accumulation intensity at the organic/organic interface. Interestingly, devices with green, blue, and white electroluminescence colors can be attained by simply replacing different ETL materials in contact with the same blue fluorophore underneath. The underlying mechanism for the color change in OLEDs will be discussed. [ABSTRACT FROM AUTHOR]

In this work, we report a series of bis-tridentate Ir(III) metal complexes, comprising a dianionic pyrazole-pyridine-phenyl tridentate chelate and a monoanionic chelate bearing a peripheral carbene and carboline coordination fragment that is linked to the central phenyl group. All these Ir(III) complexes were synthesized with an efficient one-pot and two-step method, and their emission hue was fine-tuned by variation of the substituent at the central coordination entity (i.e., pyridinyl and phenyl group) of each of the tridentate chelates. Their photophysical and electrochemical properties, thermal stabilities and electroluminescence performances are examined and discussed comprehensively. The doped devices based on [Ir(cbF)(phyz1)] (Cb1) and [Ir(cbB)(phyz1)] (Cb4) give a maximum external quantum efficiency (current efficiency) of 16.6% (55.2 cd/A) and 13.9% (43.8 cd/A), respectively. The relatively high electroluminescence efficiencies indicate that bis-tridentate Ir(III) complexes are promising candidates for OLED applications. [ABSTRACT FROM AUTHOR]

We report polymeric light-emitting diodes (PLEDs) made from pinene-substituted iridium(III) phosphorescent dopants: tris(5-(4-difluoro phenyl)-10,10-dimethyl-4-aza-tricycloundeca-2,4,6-triene) iridium (III) [Ir(F-pppy)3] and tris(5-(2,4-difluorophenyl)-10,10-dimethyl-4-aza-tricycloundeca-2,4,6-triene) iridium (III) [Ir(F2-pppy)3]. The pinene substitution introduces steric hindrance to molecular structure of the dopant that reduces triplet-triplet annihilation between dopants and consequently enhances device performance. Via endothermic energy transfer from poly(vinylcarbazole) to Ir(F-pppy)3 and Ir(F2-pppy)3, a peak electroluminescent efficiency of 32.8 cd/A or 12.3 cd/A at 12 wt % Ir(F-pppy)3 or 15 wt % Ir(F2-pppy)3 doped and solution-processed PLEDs have been obtained. These values represent significant improvement in performance over previously reported endothermic energy-transfer based electrophosphorescent devices. [ABSTRACT FROM AUTHOR]

High-efficiency nondoped white organic light-emitting devices (WOLEDs) were demonstrated by using both the intrinsic and exciplex emissions from a single electroluminescent material, 4,4′,4″-trispyrenylphenylamine (TPyPA). The simple device structure of indium tin oxide/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine/TPyPA/4,7-diphenyl-1,10-phenanthroline/LiF/Al exhibited a luminance of 10 000 cd/m2 at a low driving voltage of 4.5 V, and high current and power efficiencies of 9.4 cd/A and 9.0 lm/W, respectively. Such WOLED showed excellent color stability and purity with the Commission Internationale de L’Eclairage coordinates of (0.31, 0.35), which remained unchanged over a wide range of luminance from 100 to 20 000 cd/m2. [ABSTRACT FROM AUTHOR]

Charge-Transfer Complexes: Deep-Red/Near-Infrared Electroluminescence from Single-Component Charge-Transfer Complex via Thermally Activated Delayed Fluorescence Channel (Adv. Funct. Keywords: intermolecular charge transfer; near-infrared; organic light-emitting diode; single-component charge-transfer complex; thermally activated delayed fluorescence Intermolecular charge transfer, near-infrared, organic light-emitting diode, single-component charge-transfer complex, thermally activated delayed fluorescence. [Extracted from the article]

Formation of a single‐component charge‐transfer complex (SCCTC) is unveiled in solid state of an intermolecular charge‐transfer molecule 2‐(4‐(1‐phenyl‐1H‐phenanthro[9,10‐d]imidazol‐2‐yl)phenyl)anthracene‐9,10‐dione (PIPAQ). Intermolecular donor–acceptor interactions between two PIPAQ molecules is the primary driving force for self‐association and contributes to intermolecular charge transfer. The SCCTC character is fully verified by crystallographic, photophysical, electron spin resonance, and vibrational characterizations. The PIPAQ‐based SCCTC is first applied in light‐emitting devices as an emissive layer to realize efficient deep‐red/near‐infrared electroluminescence. This work provides new insights into SCCTC and represents an important step toward their applications in optoelectronic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A clear inverse relationship between efficiencies and dipole moments was found. • Three new blue molecules were designed and synthesized as proof-of-concept. • Record-high performance in non-doped blue OLEDs was achieved. • State-of-the-art performances were delivered in non-doped, doped and hyper-OLEDs. Non-doped and solution-processable deep blue emitters can greatly reduce the manufacturing cost of organic light-emitting diodes (OLEDs). However, influences of parameters concerning intermolecular interactions in solid state have not yet been explored. Herein, we proposed molecular dipole moment as a pre-experimental parameter to evaluate an emitter's performance in the solid state. By extracting efficiency data of OLEDs based on blue-emitting molecules from literature and calculating the dipole moments of these molecules, we found a clear inverse relationship. Three deep blue TADF emitters with similar molecular emitting properties were designed and synthesized. The PL efficiency of their solid films and device performance was found to decrease as the molecular dipole increased. Specifically, TDBA-SPQ with the smallest dipole moments of 1.86 D delivered much better performance in both vacuum-processed and solution-processed non-doped OLEDs with record-high EQE max of 22.7% and 15.2% with CIE-y coordinates of 0.136 and 0.123, respectively. [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]

A series of locally twisted dual-functional materials namely PIPT , PITT and PIFT have been designed and synthesized by introducing different polyaromatic hydrocarbon groups to a phenanthroimidazole backbone through a thiophene bridge. In these molecules, the thiophene bridge and phenanthroimidazole platform are nearly coplanar and this endows these materials with relatively shallow HOMO levels (−5.35 to −5.21 eV). On the other hand, the bulky polyaromatic hydrocarbon units introduce non-planar twisty structures which reduce molecular aggregations. These three materials show color-tunable emission (emission peak from 468 to 532 nm in film) and high thermal stability ( T g > 160 °C). Simple trilayer devices using these three phenanthroimidazole derivatives as non-doped emitting layers exhibit low turn-on voltages (2.3–2.7 V) and high maximum efficiencies of 3.74, 6.15 and 6.89 cd/A for PIPT , PITT and PIFT , respectively. Above all, owing to their shallow HOMO levels for enabling efficient hole-injection, even simpler bilayer devices employing these materials as hole-transporting emitters show low turn-on voltages (2.6–2.8 V) and high efficiencies of 5.77 cd/A for PIPT , 6.03 cd/A for PITT and 6.04 cd/A for PIFT , respectively. These comparable performances with those of the trilayer configurations show the efficient hole-injection/transport ability of these three newly developed emitters. [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]

A simple design strategy for a newclass of stable, vacuum-sublimable,and strongly emissive sky-blue neutral phosphorescent Re(I) phenanthrolinecomplexes {Re(R2phen)(CO)3[CNB(C6F5)3]} is reported. These complexes show intensebluish green emission in CH2Cl2solution withthe highest emission quantum yield and bluest emission ever reportedfor the neutral Re(I) diimine complexes. In the solid state, theydisplay sky-blue emission. The electroluminescent properties of devicescontaining these complexes have also been investigated. [ABSTRACT FROM AUTHOR]

Based on a D-π-A structuralstrategy incorporating carbazoleas a mild electron-donor and sulfone as an electron-acceptor witha π-conjugation-breaking feature, two novel blue-violet emittingmaterials (CzS1 and CzS2) were successfully designed and synthesized.The two compounds exhibit high-efficiency fluorescent emissions ofintramolecular charge-transfer transition type, with impressivelyhigh quantum yields in both solution and film states. CIEybelow 0.06 and excellent current/power efficienciesup to 1.89 cd A–1/1.58 lm W–1wereachieved with their corresponding nondoped devices. These performancescurrently represent the best results for OLEDs with CIEy< 0.06. Moreover, single-carrier devices werealso fabricated to demonstrate the bipolar characteristics as wellas to understand the different electroluminescence performance ofthe two fluorophores. [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]

Abstract: A high-efficiency, undoped, blue, organic light-emitting device was devised that employed a novel electroluminescent material 4-(7,10-diphenylfluoranthen-8-yl)-N,N-diphenylbenzenamine as electrofluorescence emitter. The device with a simple structure of ITO/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine/4-(7,10-diphenylfluoranthen-8-yl)-N,N-diphenylbenzenamine/4,7-diphenyl-1,10-phenanthroline/LiF/Al exhibited stable blue light emission of CIE chromaticity coordinates (x =0.19±0.01 and y =0.45±0.02), and a current efficiency of 6.0cd A−1 and a power efficiency of 4.6lm W−1. [Copyright &y& Elsevier]

Abstract: A high-efficiency nondoped green organic light-emitting device was demonstrated by using a novel electroluminescent material 3,6-di[8-(7,10-diphenylfluoranthenyl)] phenyl-9-[8-(7,10-diphenylfluoranthenyl)] phenylcarbazole (TDPFPC) as an efficient electrofluorescence emitter. The device with a simple structure of ITO/α-napthylphenylbiphenyl diamine/TDPFPC/4,7-diphenyl-1,10-phenanthroline/LiF/Al exhibited green emission with Commission Internationale de L’Eclairage coordinates of (0.25, 0.49), a high current efficiency of 10.1cd/A, and a high power efficiency of 12.1lm/W. [Copyright &y& Elsevier]

Abstract: A new compound with intramolecular charge transfer (ICT) property—5,6-Bis-[4-(naphthalene-1-yl-phenyl-amino)-phenyl]-pyrazine-2,3-dicarbonitrile(BNPPDC) was synthesized. The new compound was strongly fluorescent in non-polar and moderately polar solvents, as well as in thin solid film. The absorption and emission maxima shifted to longer wavelength with increasing solvent polarity. The fluorescence quantum yield also increased with increasing solvent polarity from non-polar to moderately polar solvents, then decreased with further increase of solvent polarity. This indicates both “positive” and “negative” solvatokinetic effects co-existed. Using this material as hole-transporting emitter and host emitter, we fabricated two electroluminescent (EL) devices with structures of A (ITO/BNPPDC (45nm)/1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) (45nm)/Mg:Ag (200nm) and B (ITO/N,N′-diphenyl-N,N′-bis-(3-methylphenyl) (1,1′-diphenyl)4,4′-diamine (TPD) (50nm)/BNPPDC (20nm)/1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) (45nm)/Mg:Ag (200nm). The devices showed green-yellow EL emission with good efficiency and high brightness. For example, the device A exhibited a high brightness of 17400cd/m2 at a driving voltage of 11V and a very low turn-on voltage (2.9V), as well as a maximum luminous efficiency 3.61cd/A. The device B showed a similar performance with a high brightness of 12650cd/m2 at a driving voltage of 13V and a maximum luminous efficiency 3.62cd/A. In addition, the EL devices using BNPPDC as a host and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as a dopant (configuration: ITO/TPD (60nm)/BNPPDC:DCJTB (2%) (30nm)/TPBI (35nm)/Mg:Ag (200nm)) showed a good performance with a brightness of 150cd/m2 at 4.5V, a maximum brightness of 12600cd/m2 at 11.5V, and a maximum luminous efficiency of 3.30cd/A. [Copyright &y& Elsevier]

Abstract: A new phenazine dye—3-methyl-8-dimethylaminophenazine (MDAP) with intramolecular charge transfer (ICT) property was synthesized. The photoluminescence and electroluminescence of were investigated. The device with a configuration of ITO/TPD (30nm)/TPD:MDAP (30nm)/Alq3:MDAP (35nm)/Alq3 (30nm)/Mg:Ag (200nm) showed a good performance with a brightness of 21650cd/m2 at 250mA/cm2, a maximum luminous efficiency of 9.97cd/A and a yellow emission peaked at about 564–586nm. [Copyright &y& Elsevier]

[Display omitted] • Molecular design of anthracene-based deep-blue fluorescent emitter is presented. • External quantum efficiency improvement is achieved by TTA. • High efficiency with small roll-off in deep-blue nondoped OLED is realized. Three new anthracene-based emitters, 4-(10-(9,9′-spirobi[fluoren]-2-yl)anthracen-9-yl)benzonitrile (SBF - AnCN), 4-(10-(9,9-diphenyl-9 H -fluoren-2-yl)anthracen-9-yl)benzonitrile (DPF-AnCN) and 4-(10-(9,9-dimethyl-9 H -fluoren-2-yl)anthracen-9-yl)benzonitrile (DMF-AnCN) are developed for deep blue organic light-emitting diodes (OLEDs). Their photophysical properties, thermal properties, molecular configurations and device performances have been systematically investigated. As verified by crystallographic study, these anthracene derivatives possess highly twisted configuration, leading to deep-blue light emission by restraining π-conjugation extension. Furthermore, the difference in the molecular packing manner may influence the photoluminescence quantum yields (PLQYs) in solid state and the proportion of singlet exciton harvested by triplet–triplet annihilation (TTA) process. A nondoped device fabricated using DPF-AnCN as emitter exhibits a maximum external quantum efficiency (EQE) of 7.1% with insignificant efficiency roll-off (6.6%@1000 nit) and Commission Internationale de L'Eclairage (CIE) index of (0.149, 0.104), approaching the standard blue index of the National Television System Committee (NTSC) of (0.14, 0.08). It is demonstrated that TTA is responsible for the excellent electroluminescence (EL) performance. In comparison with doped OLEDs, transient EL decay measurements demonstrate that TTA process is more efficient in the nondoped device. This work would provide an efficient method for designing deep-blue nondoped EL materials. [ABSTRACT FROM AUTHOR]

• Two sterically shielded anthracene derivatives are developed with modification of peripheral phenyl groups (PPGs). • The influence of PPGs decoration on the photoluminescence and electroluminescence properties is studied to unveil the structure-property relationship. • PPGs can significantly suppress electronic coupling in solid state due to its steric-demanding geometry • High efficiency with EQE of up to 5.05% and deep-blue electroluminescence with color index of (0.15, 0.09) are demonstrated. Two new anthracene derivatives are designed with a sterically shielded strategy for deep-blue electroluminescence applications. The naphthyl groups of the widely used blue emitter 9,10-di-(2-naphthyl)anthracene (ADN) were modified with four peripheral phenyl groups (PPGs) to enhance intermolecular spacing in solid-state thin film for suppressing electronic coupling. Influence of the PPGs decoration on photoluminescence and electroluminescence are investigated to reveal the structure-property relationship. A nondoped organic light-emitting diode with the new emitter 9-(naphthalen-2-yl)-10-(5,6,7,8-tetraphenylnaphthalen-2-yl)anthracene (M1) exhibits excellent performance with a maximum external quantum efficiency of 5.05% and deep-blue color index of (0.15, 0.09). Although the use of bulky peripheral substituents does improve device performance, it should be paid attention to the non-conductive effect induced by the larger molecular spacing in the design of deep-blue electroluminescence materials. This work provides a promising molecular design for deep-blue electroluminescence materials. [Display omitted] [ABSTRACT FROM AUTHOR]