Self-Host Blue-Emitting Iridium Dendrimer with Carbazole Dendrons: Nondoped Phosphorescent Organic Light-Emitting Diodes

Asymmetrical-Dendronized TADF Emitters for Efficient Non-doped Solution-Processed OLEDs by Eliminating Degenerate Excited States and Creating Solely Thermal Equilibrium Routes

The mechanism of thermally activated delayed fluorescence (TADF) in dendrimers is not clear. We report that fully‐conjugated or fully‐nonconjugated structures cause unwanted degenerate excited states due to multiple identical dendrons, which limit their TADF efficiency. We have synthesized asymmetrical “half‐dendronized” and “half‐dendronized‐half‐encapsulated” emitters. By eliminating degenerate excited states, the triplet locally excited state is ≥0.3 eV above the lowest triplet charge‐transfer state, assuring a solely thermal equilibrium route for an effective spin‐flip process. The isolated encapsulating tricarbazole unit can protect the TADF unit, reducing nonradiative decay and enhancing TADF performance. Non‐doped solution‐processed devices reach a high external quantum efficiency (EQE_max) of 24.0 % (65.9 cd A⁻¹, 59.2 lm W⁻¹) with CIE coordinates of (0.24, 0.45) with a low efficiency roll‐off and EQEs of 23.6 % and 21.3 % at 100 and 500 cd m⁻².

Rational Design of π-Conjugated Tricoordinated Organoboron Derivatives With Thermally Activated Delayed Fluorescent Properties for Application in Organic Light-Emitting Diodes

A series of donor–acceptor (D–A) tricoordinated organoboron derivatives (1–10) have been systematically investigated for thermally activated delayed fluorescent (TADF)-based organic light-emitting diode (OLED) materials. The calculated results show that the designed molecules exhibit small singlet-triplet energy gap (ΔE_ST) values. Density functional theory (DFT) analysis indicated that the designed molecules display an efficient separation between donor and acceptor fragments because of a small overlap between donor and acceptor fragments on HOMOs and LUMOs. Furthermore, the delayed fluorescence emission color can be tuned effectively by introduction of different polycyclic aromatic fragments in parent molecule 1. The calculated results show that molecules 2, 3, and 4 possess more significant Stokes shifts and red emission with small ΔE_ST values. Nevertheless, other molecules exhibit green (1, 7, and 8), light green (6 and 10), and blue (5 and 9) emissions. Meanwhile, they are potential ambipolar charge transport materials except that 4 and 10 can serve as electron and hole transport materials only, respectively. Therefore, we proposed a rational way for the design of efficient TADF materials as well as charge transport materials for OLEDs simultaneously.

Targeting G-Rich DNA Structures with Photoreactive Bis-Cyclometallated Iridium(III) Complexes

The synthesis and characterisation of three novel iridium(III) bis-cyclometallated complexes is reported. Their photophysics have been fully characterised by classical methods and revealed charge-transfer (CT) and ligand-centred (LC) transitions. Their ability to selectively interact with G-quadruplex telomeric DNA over duplex DNA has been studied by circular dichroism (CD), bio-layer interferometry (BLI) and surface plasmon resonance (SPR) analyses. Interestingly, one of the complexes was able to promote photoinduced electron transfer (PET) with the guanine DNA base, which in turn led to oxidative damage (such as the formation of 8-oxoguanine) to the telomeric sequence. To the best of our knowledge, this is the first study of highly photo-oxidising bis-cyclometallated iridium(III) complexes with G-quadruplex telomeric DNA.

Creation of Efficient Blue Aggregation-Induced Emission Luminogens for High-Performance Nondoped Blue OLEDs and Hybrid White OLEDs

Organic blue luminescent materials are essential for organic light-emitting diodes (OLEDs). However, high-quality blue materials that can fulfill the requirements of OLED commercialization are much rare. Herein, two novel blue luminogens, 9-(4-(2,6-di- tert-butyl-10-(4-(1,2,2-triphenylvinyl)phenyl)anthracen-9-yl)phenyl)-9 H-carbazole and 9-(4-(2,6-di- tert-butyl-10-(4-(1,2,2-triphenylvinyl)phenyl)anthracen-9-yl)1,3-di(9 H-carbazol-9-yl)benzene (TPE-TADC), consisting of anthracene, tetraphenylethene, and carbazole groups are successfully prepared, and their thermal, optical, electronic, and electrochemical properties are fully investigated. They exhibit prominent aggregation-induced emission property and strong blue fluorescence at ∼455 nm in neat films. Efficient nondoped OLEDs are fabricated with these blue luminogens, providing blue electroluminescence (EL) at 451 nm (CIE _{x, y} = 0.165, 0.141) and high EL efficiencies of 6.81 cd A^-1, 6.57 lm W^-1, and 5.71%. By utilizing TPE-TADC as a blue emissive layer, high-performance two-color hybrid white OLEDs are achieved, furnishing modulatable light color from pure white (CIE _{x, y} = 0.33, 0.33) to warm white (CIE _{x, y} = 0.44, 0.46) and excellent EL efficiencies of 56.7 cd A^-1, 55.2 lm W^-1, and 19.2%. More importantly, these blue and white OLEDs all display ultrahigh color and efficiency stabilities at high luminance, indicating the great potential of these blue luminogens for the application in OLED displays and white illumination.

Recent Advances in the Optimization of Organic Light-Emitting Diodes with Metal-Containing Nanomaterials

Metal-containing nanomaterials have attracted widespread attention in recent years due to their physicochemical, light-scattering and plasmonic properties. By introducing different kinds and different structures of metal-containing nanomaterials into organic light-emitting diodes (OLEDs), the optical properties of the devices can be tailored, which can effectively improve the luminous efficiency of OLEDs. In this review, the fundamental knowledge of OLEDs and metallic nanomaterials were firstly introduced. Then we overviewed the recent development of the optimization of OLEDs through introducing different kinds of metal-containing nanomaterials.

High efficiency green OLEDs based on homoleptic iridium complexes with steric phenylpyridazine ligands

The doped and non-doped OLED devices based on 3 exhibit very high EQE of 25.2% and 15.2%, respectively.

An Unconventional Approach to Induce Liquid-Crystalline Phases of Triazine-Based Dendrons by Breaking Their Self-Assembly into Dimers

Three triazine-based dendrons (1 a-c) were successfully prepared in 70-83 % yields. These newly prepared dendrons are found to be liquid crystalline (LC). Computational investigations on molecular conformations and dipoles of triazine-based dendrons reveal that the substituent on the central triazine unit interrupts strong dipole or H-bond interactions to avoid dimeric formation. The obtained dendrons, not favouring self-assembly into dimers but showing LC behaviours, provides evidence for an approach contrary to the conventional method of inducing LC behaviours of dendrons by dimer or trimer formation, mostly through H-bond interactions.