Organic materials that exhibit thermally activated delayed fluorescence (TADF) are an attractive class of functional materials that have witnessed a booming development in recent years. Since Adachi et al. reported high-performance TADF-OLED devices in 2012, there have been many reports regarding the design and synthesis of new TADF luminogens, which have various molecular structures and are used for different applications. In this review, we summarize and discuss the latest progress concerning this rapidly developing research field, in which the majority of the reported TADF systems are discussed, along with their derived structure–property relationships, TADF mechanisms and applications. We hope that such a review provides a clear outlook of these novel functional materials for a broad range of scientists within different disciplinary areas and attracts more researchers to devote themselves to this interesting research field.

Recent advances in organic thermally activated delayed fluorescence materials.

The present invention provides a heterocyclic compound and an organic light-emitting device including the heterocyclic compound. The organic light-emitting devices using the heterocyclic compounds have high-efficiency, low driving voltage, high luminance and long lifespan.

Organic light-emitting device

We thank the University of St Andrews for support. EZ-C thanks the Leverhulme Trust for financial support (RPG-2016-047). and the EPSRC (EP/P010482/1) for financial support.

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Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes.

Although organic light-emitting devices have been commercialized as flat panel displays since 1997, only singlet excitons were emitted. Full use of singlet and triplet excitons, electrophosphorescence, has attracted increasing attentions after the premier work made by Forrest, Thompson, and co-workers. In fact, red electrophosphorescent dye has already been used in sub-display of commercial mobile phones since 2003. Highly efficient green phosphorescent dye is now undergoing of commercialization. Very recently, blue phosphorescence approaching the theoretical efficiency has also been achieved, which may overcome the final obstacle against the commercialization of full color display and white light sources from phosphorescent materials. Combining light out-coupling structures with highly efficient phosphors (shown in the table-of-contents image), white emission with an efficiency matching that of fluorescent tubes (90 lm/W) has now been realized. It is possible to tune the color to the true white region by changing to a deep blue emitter and corresponding wide gap host and transporting material for the blue phosphor. In this article, recent progresses in red, green, blue, and white electrophosphorescent materials for OLEDs are reviewed, with special emphasis on blue electrophosphorescent materials.

Recent Progresses on Materials for Electrophosphorescent Organic Light-Emitting Devices

Phosphorescent organic light-emitting diodes (PhOLEDs) unfurl a bright future for the next generation of flat-panel displays and lighting sources due to their merit of high quantum efficiency compared with fluorescent OLEDs. This critical review focuses on small-molecular organic host materials as triplet guest emitters in PhOLEDs. At first, some typical hole and electron transport materials used in OLEDs are briefly introduced. Then the hole transport-type, electron transport-type, bipolar transport host materials and the pure-hydrocarbon compounds are comprehensively presented. The molecular design concept, molecular structures and physical properties such as triplet energy, HOMO/LUMO energy levels, thermal and morphological stabilities, and the applications of host materials in PhOLEDs are reviewed (152 references).

Organic host materials for phosphorescent organic light-emitting diodes

We have significantly improved the emission efficiency in an organic light-emitting device (OLED) based on iridium (III)bis[(4,6-di-fluoropheny)-pyridinato-N,C2′]picolinate (FIrpic). To improve the efficiency, 4,4′-bis(9-carbazolyl)-2,2′-dimethyl-biphenyl, which has a high triplet energy, was used as the carrier-transporting host for the emissive layer. The FIrpic-based OLED exhibited a maximum external quantum efficiency of 10.4%, corresponding to a current efficiency of 20.4 cd/A, and a maximum power efficiency of 10.5 lm/W. The efficiency was drastically improved compared to that of a previously reported FIrpic-based OLED. This result indicates that triplet energy is efficiently confined on FIrpic molecules, resulting in the high efficiency.

Confinement of triplet energy on phosphorescent molecules for highly-efficient organic blue-light-emitting devices

PROBLEM TO BE SOLVED: To provide an organic electroluminescent element of excellent luminous efficiency with a long service life, and a display device of low power consumption with a long service life using the organic electroluminescent element. SOLUTION: This organic electroluminescent element with an organic layer clamped between two electrodes contains a compound expressed by a general formula (1), in at least one layer of the organic layer. In the formula, B represents a boron atom, C represents a carbon atom, A11 , A12 and A13 represent a carbon atom or a nitrogen atom, Z11 , Z12 and Z13 represent an atomic group required to complete an aromatic ring, R11 , R12 and R13 independently represent an alkyl group, an alkyloxy group, an aryloxy group or an halogen atom, R14 , R15 and R16 independently represent a hydrogen atom or a monovalent substituent, and l, m, n independently represent 0-7.

Organic electroluminescent element and display device

Disclosed is an organic electroluminescent device material which is characterized by containing a platinum complex represented by the general formula (1) wherein a nitrogen-containing group is introduced at the 4-position of a phenyl pyridine, which is a ligand of the platinum complex, and a specific substituent is further introduced at a specific position thereof. In the general formula (1) shown in the description, R1, R2, R3, R4, R5, R6 and R7 respectively represent a hydrogen atom or a substituent, and at least one of R1, R2, R3 and R4 represents an electron-donating group. Also disclosed are an organic EL device, illuminating device and display using such an organic electroluminescent device material.

Organic electroluminescent device material, organic electroluminescent device, display and illuminating device

An organic electroluminescent device comprising at least a light-emitting layer containing a phosphorescent compound between an anode and a cathode is characterized by comprising an adjoining layer so arranged between the light-emitting layer and the cathode as to be adjacent to the light-emitting layer and containing a compound with an electron-withdrawing group having an HOMO in the range from -5.7 eV to -7.0 eV and an LUMO in the range from -1.3 eV to -2.3 eV.

Organic electroluminescent device, illuminating device, and display

The present invention provides: an organic EL element exhibiting high luminance, a high external quantum efficiency and a long high temperature driving life at 50° C.; an illuminator and a display device employing the organic EL element; and a material preferably used for the organic EL element.

Hiroshi Kita

Papers

Confinement of triplet energy on phosphorescent molecules for highly-efficient organic blue-light-emitting devices

Organic electroluminescent element and display device

Organic electroluminescent device material, organic electroluminescent device, display and illuminating device

Organic electroluminescent device, illuminating device, and display

Material for organic electroluminescent device, organic electroluminescent device, illuminating device and display