Supramolecular Sky‐Blue Phosphorescent Polymer Iridium Complexes for Single‐Emissive‐Layer Organic Light‐Emitting Diodes

Novel supramolecular phosphorescent polymers (SPPs) are synthesized as a new class of solution‐processable electroluminescent emitters. The formation of these SPPs takes advantage of the efficient non‐bonding assembly between bis(dibenzo‐24‐crown‐8)‐functionalized iridium complex monomer and bis(dibenzylammonium)‐tethered co‐monomer, which is monitored by ¹H NMR spectroscopy and viscosity measurements. These SPPs show good film morphology and an intrinsic glass transition with a T_g of 94–116 °C. Noticeably, they are highly photoluminescent in solid state with quantum efficiency up to ca. 78%. The photophysical and electroluminescent properties are strongly dependent on the molecular structures of the iridium complex monomers.

     

高效磷光铱配合物的合成及电致发光性能研究

合成了一种含苯并噻唑结构配体的环金属化铱配合物(ffbi)₂Ir(acac)，(其中ffbi为1-(4-氟苄基)-2-(4-氟苯基)苯并咪唑，acac为乙酰丙酮)，并以其作为发光体, 制备了有机电致发光器件。结果表明该配合物具有强磷光发光特性，器件发绿色光。其中结构为TCTA(40 nm)/CBP∶Ir(6.3%，30 nm)/BCP(10 nm)/Alq(40 nm)的电致发光器件在12 V电压下最大发光亮度达41 499 cd·m^-2，在8 V电压下，最大外量子效率达5.7%。     

Red‐Emitting Dendritic Iridium(III) Complexes for Solution Processable Phosphorescent Organic Light‐Emitting Diodes

Functionalization of a red phosphorescent iridium(III) complex core surrounded by rigid polyphenylene dendrons with a hole‐transporting triphenylamine surface allows to prevent the intermolecular aggregation‐induced emission quenching, improves charge recombination, and therefore enhances photo‐ and electroluminescence efficiencies of dendrimer in solid state. These multifunctional shape‐persistent dendrimers provide a new pathway to design highly efficient solution processable materials for phosphorescent organic light‐emitting diodes (PhOLEDs).     

An Easy Route to Red Emitting Homoleptic IrIII Complex for Highly Efficient Solution‐Processed Phosphorescent Organic Light‐Emitting Diodes

A thiophene‐phenylquinoline‐based homoleptic Ir^III complex, [Ir(Th‐PQ)₃], has been synthesised by a simple route and utilised as a dopant in solution‐processed phosphorescent organic light‐emitting diodes (PhOLEDs). It shows the current efficiency of approximately 26 cd A^?1 and the external quantum efficiency of about 21 %, which are the highest values reported to date for PhOLEDs prepared by solution‐process.     

Syntheses,Photophysics, and Application of Iridium(III) Phosphorescent Emitters for Highly Efficient,Long‐Life Organic Light‐Emitting Diodes

Long live the OLED! Rational design and synthesis of Ir^III complexes bearing two cyclometalated ligands (C N) and one 2‐(diphenylphosphino)phenolate chelate (P O) as well as the corresponding Ir^III derivatives with only one (C N) ligand and two P O chelates are reported. According to the observed photophysical data, a P O ligand is found to be able to fine‐tune the light‐emitting electronic transition of these complexes.

     

Bipolar Host Materials for Organic Light‐Emitting Diodes

It is important to balance holes and electrons in the emitting layer of organic light‐emitting diodes to maximize recombination efficiency and the accompanying external quantum efficiency. Therefore, the host materials of the emitting layer should transport both holes and electrons for the charge balance. From this perspective, bipolar hosts have been popular as the host materials of thermally activated delayed fluorescent devices and phosphorescent organic light‐emitting diodes. In this review, we have summarized recent developments of bipolar hosts and suggested perspectives of host materials for organic light‐emitting diodes.     

Recent Progress in Sublimable Cationic Iridium(III) Complexes for Organic Light‐Emitting Diodes

Sublimable cationic iridium(III) complexes consisting of light‐emitting coordinated iridium(III) cations and nonluminous negative counter‐ions, show excellent photophysical properties, superior electrochemical behaviors and high thermal stabilities, therefore have emerged as a new library of phosphorescent materials for various organic optoelectronic devices. Here we summarize and highlight the recent progress in sublimable cationic iridium(III) complexes, regarding the material design strategies, synthetic routes, photoluminescent characteristics in both solutions and neat films, together with the current utilization in organic light‐emitting diodes based on the emissive material layers fabricated by vacuum evaporation deposition. Finally, we present a brief outlook thereon, indicating the great promise and brilliant application prospect of sublimable cationic iridium(III) complexes in future flat‐panel display and solid‐state lighting technology.     

Photoprogrammable Organic Light‐Emitting Diodes

Enlightening the memory : The integration of a crosslinkable photochromic dithienylperfluorocyclopentene (DTE) into organic light‐emitting diodes (OLED) allows for the individualization of the emissive area of the OLED device, for example, for signage applications. The operation principle is based on switching the injection barrier for holes (positive charge carriers). Very large ON/OFF ratios of up to 3000 for current as well as electroluminescence have been achieved.

     

White Polymer Light‐Emitting Diodes Based on Star‐Shaped Polymers with an Orange Dendritic Phosphorescent Core

A series of new star‐shaped polymers with a triphenylamine‐based iridium(III) dendritic complex as the orange‐emitting core and poly(9,9‐dihexylfluorene) (PFH) chains as the blue‐emitting arms is developed towards white polymer light‐emitting diodes (WPLEDs). By fine‐tuning the content of the orange phosphor, partial energy transfer and charge trapping from the blue backbone to the orange core is realized to achieve white light emission. Single‐layer WPLEDs with the configuration of ITO (indium‐tin oxide)/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/polymer/CsF/Al exhibit a maximum current efficiency of 1.69 cd A⁻¹ and CIE coordinates of (0.35, 0.33), which is very close to the pure white‐light point of (0.33, 0.33). To the best of our knowledge, this is the first report on star‐shaped white‐emitting single polymers that simultaneously consist of fluorescent and phosphorescent species.

     

Doping‐Free White Organic Light‐Emitting Diodes

Doping‐free white organic light‐emitting diodes (WOLEDs) have great potential to the next‐generation solid‐state lighting and displays due to the excellent properties, such as high efficiency, bright luminance, low power consumption, simplified structure and low cost. In this account, our recent developments on doping‐free WOLEDs have been summarized. Firstly, fundamental concepts of doping‐free WOLEDs have been described. Then, the effective strategies to develop doping‐free WOLEDs have been presented. Particularly, the manipulation of charges and excitons distribution in different kinds of doping‐free WOLEDs have been highlighted, including doping‐free fluorescent/phosphorescent hybrid WOLEDs, doping‐free thermally activated delayed fluorescent WOLEDs and doping‐free phosphorescent WOLEDs. In the end, an outlook for the future development of doping‐free WOLEDs have been clarified.     

Constructing a Novel Dendron for a Self‐Host Blue Emitter with Thermally Activated Delayed Fluorescence: Solution‐Processed Nondoped Organic Light‐Emitting Diodes with Bipolar Charge Transfer and Stable Color Purity

Self‐host thermally activated delayed fluorescence (TADF) materials have recently been identified as effective emitters for solution‐processed nondoped organic light‐emitting diodes (OLEDs). However, except for the carbazole unit, few novel dendrons have been developed to build self‐host TADF emitters. This study reports two self‐host blue materials, tbCz‐SO and poCz‐SO, with the same TADF emissive core and different dendrons. The influence of the peripheral dendrons on the photophysical properties and electroluminescent performances of the self‐host materials were systematically investigated. The transient fluorescence and electroluminescence spectra indicated that the diphenylphosphoryl carbazole units could effectively encapsulate the emissive core to reduce the concentration quenching effect and to enhance reverse intersystem crossing. By using tbCz‐SO and poCz‐SO as host‐free blue emitters, the performance of the solution‐processed nondoped OLED device demonstrated that a more balanced charge transfer from the bipolar dendrons would offer a better current efficiency of 10.5 cd A⁻¹ and stable color purity with Commission Internationale de L'Eclairage units of (0.18, 0.27).     

Saturated Red‐Light‐Emitting Gold(III) Triphenylamine Dendrimers for Solution‐Processable Organic Light‐Emitting Devices

A novel isoquinoline‐containing C^N^C ligand and its phosphorescent triphenylamine‐based alkynylgold(III) dendrimers have been synthesized. These alkynylgold(III) dendrimers serve as phosphorescent dopants in the fabrication of efficient solution‐processable organic light‐emitting devices (OLEDs). The photophysical, electrochemical, and electroluminescence properties were studied. A saturated red emission with CIE coordinates of (0.64, 0.36) and a high EQE value of 3.62 % were achieved. Unlike other red‐light‐emitting iridium(III) dendrimers, a low turn‐on voltage of less than 3 V and a reduced efficiency roll‐off at high current densities were observed; this can be accounted for by the enhanced carrier transporting ability and the relatively short lifetimes in the high‐generation dendrimers. This class of alkynylgold(III) dendrimers are promising candidates as phosphorescent dopants in the fabrication of solution‐processable OLEDs.     

Molecular Orientation Effects in Organic Light‐Emitting Diodes

It is well known that by horizontally aligning the transition dipole moments of exciton dipoles in the emitter films of organic light‐emitting diodes (OLEDs), a larger fraction of the radiative power can escape from the OLED stack, increasing the light outcoupling efficiency by up to 50 % compared to the isotropic counterparts. In this account, we review recent advances in understanding this phenomenon, with a special focus on the practical strategies to control the molecular orientation in vacuum‐deposited films of thermally activated delayed fluorescent (TADF) dyes. The role of molecular orientation in efficient OLED design is discussed, which has been experimentally proven to increase the external quantum efficiency exceeding 30 %. We outline the future challenges and perspectives in this field, including the potential to extend the concept to the solution‐processed films. Finally, the development of multiscale computer simulations is reviewed to assess their potential as a complementary approach to systematically screening OLED molecules in silico.     

High Power Efficiency Blue‐to‐Green Organic Light‐Emitting Diodes Using Isonicotinonitrile‐Based Fluorescent Emitters

Herein, 9,10‐dihydro‐9,9‐dimethylacridine (Ac) or phenoxazine (PXZ)‐substituted isonicotinonitrile (INN) derivatives, denoted as 2AcINN , 26AcINN , and 26PXZINN , were developed as a series of thermally activated delayed fluorescence (TADF) emitters. These emitters showed reasonably high photoluminescence quantum yields of 71–79 % in the host films and high power efficiency organic light‐emitting diodes (OLEDs). Sky‐blue emitter 26AcINN exhibited a low turn‐on voltage of 2.9 V, a high external quantum efficiency (η _ext) of 22 %, and a high power efficiency (η _p) of 66 lm W⁻¹ with Commission Internationale de l′Eclairage (CIE) chromaticity coordinates of (0.22, 0.45), whereas green emitter 26PXZINN exhibited a low turn‐on voltage of 2.2 V, a high η _ext of 22 %, and a high η _p of 99 lm W⁻¹ with CIE chromaticity coordinates of (0.37, 0.58). These performances are among the best for TADF OLEDs to date.