Versatile Synthesis of Luminescent Tetradentate Cyclometalated Alkynylgold(III) Complexes and Their Application in Solution‐Processable Organic Light‐Emitting Devices

A new class of cyclometalated tetradentate alkynylgold(III) complexes has been successfully synthesized by post‐synthetic modification. Through the judicious design and choice of pincer ligands, post‐synthetic cyclization could be achieved to produce the robust and structurally rigid class of tetradentate gold(III) C^N^C^C complexes with high photoluminescence quantum yields of up to 0.49 in solution and 0.78 in doped thin films at room temperature, at least an order of magnitude higher than those of the structurally related uncyclized tridentate alkynylgold(III) analogues. High‐performance yellow to orange‐red emitting solution‐processable organic light‐emitting devices have also been achieved with external quantum efficiency of 11.1 %. This work describes for the first time of the use of post‐synthetic ligand modification approach to overcome the synthetic challenge for tetradentate alkynylgold(III) complexes.     

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.

     

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).     

Adamantane‐Substituted Acridine Donor for Blue Dual Fluorescence and Efficient Organic Light‐Emitting Diodes

To date, blue dual fluorescence emission (DFE) has not been realized because of the limited choice of chemical moieties and severe geometric deformation of the DFE emitters leading to strong intramolecular charge transfer (ICT) with a large Stokes shift in excited states. Herein, an emitter (1′r,5′R,7′S)‐10‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐10H‐spiro [acridine‐9,2′‐adamantane] (a‐DMAc‐TRZ) containing a novel adamantane‐substituted acridine donor is reported, which exhibits unusual blue DFE. The introduction of the rigid and bulky adamantane moiety not only suppressed the geometry relaxation in excited state, but also induced the formation of quasi‐axial conformer (QAC) and quasi‐equatorial conformer (QEC) geometries, leading to deep‐blue conventional fluorescence and sky‐blue thermally activated delayed fluorescence (TADF). The resulting organic light‐emitting diodes (OLEDs) achieved a maximum external quantum efficiency (EQE) of about 29 %, which is the highest reported for OLEDs based on dual‐conformation emitters.     

One‐Step Borylation of 1,3‐Diaryloxybenzenes Towards Efficient Materials for Organic Light‐Emitting Diodes

The development of a one‐step borylation of 1,3‐diaryloxybenzenes, yielding novel boron‐containing polycyclic aromatic compounds, is reported. The resulting boron‐containing compounds possess high singlet‐triplet excitation energies as a result of localized frontier molecular orbitals induced by boron and oxygen. Using these compounds as a host material, we successfully prepared phosphorescent organic light‐emitting diodes exhibiting high efficiency and adequate lifetimes. Moreover, using the present one‐step borylation, we succeeded in the synthesis of an efficient, thermally activated delayed fluorescence emitter and boron‐fused benzo[6]helicene.     

Aromatic‐Imide‐Based Thermally Activated Delayed Fluorescence Materials for Highly Efficient Organic Light‐Emitting Diodes

Aromatic‐imide‐based thermally activated delayed fluorescence (TADF) materials with a twisted donor–acceptor–donor skeleton were efficiently synthesized and exhibited excellent thermal stability and high photoluminescence quantum yields. The small ΔE _ST value (<0.1 eV) along with the clear temperature‐dependent delayed component of their transient photoluminescence (PL) spectra demonstrated their excellent TADF properties. Moreover, the performance of organic light‐emitting diodes in which TADF materials AI‐Cz and AI‐TBCz were used as dopants were outstanding, with external quantum efficiencies up to 23.2 and 21.1 %, respectively.     

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.     

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.     

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.     

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.     

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.

     

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

Higher efficiency in the end‐use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid‐state electroluminescent materials and belong to the general area of solid‐state lighting (SSL). The two main technologies being developed in SSL are light‐emitting diodes (LEDs) and organic light‐emitting diodes (OLEDs), but in recent years, light‐emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition‐metal complexes (iTMCs). Cyclometalated complexes of Ir^III are by far the most utilized class of iTMCs in LECs. Herein, we show how these complexes can be prepared and discuss their unique electronic, photophysical, and photochemical properties. Finally, the progress in the performance of iTMCs based LECs, in terms of turn‐on time, stability, efficiency, and color is presented.