Pure Hydrocarbon Materials as Highly Efficient Host for White Phosphorescent Organic Light-Emitting Diodes: A New Molecular Design Approach.

To date, all efficient host materials reported for phosphorescent OLEDs (PhOLEDs) are constructed with heteroatoms, which have a crucial role in the device performance. However, it has been shown in recent years that the heteroatoms not only increase the design complexity but can also be involved in the instability of the PhOLED, which is nowadays the most important obstacle to overcome. Herein, we design pure aromatic hydrocarbon materials (PHC) as very efficient hosts in high-performance white and blue PhOLEDs. With EQE of 27.7 %, the PHC-based white PhOLEDs display similar efficiency as the best reported with heteroatom-based hosts. Incorporated as a host in a blue PhOLED, which are still the weakest links of the technology, a very high EQE of 25.6 % is reached, surpassing, for the first time, the barrier of 25 % for a PHC and FIrpic blue emitter. This performance shows that the PHC strategy represents an effective alternative for the future development of the OLED industry.

Altererythrobacter flava sp. nov., a new member of the family Erythrobacteraceae, isolated from a surface seawater sample.

A Gram-stain-negative, light yellow pigmented, non-motile and aerobic bacterial strain, designated HHU E2-1 T, was isolated from a surface seawater sample. The 16S rRNA gene sequence analysis indicated that HHU E2-1 T shared the highest sequence similarity to the type strain Qipengyuania gaetbuli DSM 16225 T (96.90%), which belongs to the family Erythrobacteraceae. Combined phylogeny of 288 single-copy orthologous gene clusters, analysis of average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH), average amino acid identity (AAI) and evolutionary distances suggested that HHU E2-1 T can be considered as a member of the genus Altererythrobacter based on the recently proposed standard for defining genera of Erythrobacteraceae. Strain HHU E2-1 T grew at 15-35 °C and pH 5.0-8.0, with optimum growth at 28 °C and pH 7.0. Tolerance to NaCl was up to 4% (w/v) with optimum growth in 2-3% NaCl. The major fatty acids (> 10%) were C18:1ω7c11-methyl, summed feature 3 (C16:1ω7c and/or C16:1ω6c), and summed feature 8 (C18:1ω7c and/or C18:1ω6c). The predominant isoprenoid quinone was ubiquinone-10. The genomic G + C content was 57.40%. On the basis of the phenotypic, phylogenetic and chemotaxonomic characterizations, HHU E2-1 T represents a novel species of the genus Altererythrobacter, for which the name Altererythrobacter flava sp. nov. is proposed. The type strain is HHU E2-1 T (= CGMCC 1.17394 T = KCTC 72835 T = MCCC 1K04226T).

High-Efficiency Red Organic Light-Emitting Diodes with External Quantum Efficiency Close to 30% Based on a Novel Thermally Activated Delayed Fluorescence Emitter.

Researchers have spared no effort to design new thermally activated delayed fluorescence (TADF) emitters for high-efficiency organic light-emitting diodes (OLEDs). However, efficient long-wavelength TADF emitters are rarely reported. Herein, a red TADF emitter, TPA-PZCN, is reported, which possesses a high photoluminescence quantum yield (ΦPL ) of 97% and a small singlet-triplet splitting (ΔEST ) of 0.13 eV. Based on the superior properties of TPA-PZCN, red, deep-red, and near-infrared (NIR) OLEDs are fabricated by utilizing different device structure strategies. The red devices obtain a remarkable maximum external quantum efficiency (EQE) of 27.4% and an electroluminescence (EL) peak at 628 nm with Commission Internationale de L'Eclairage (CIE) coordinates of (0.65, 0.35), which represents the best result with a peak wavelength longer than 600 nm among those of the reported red TADF devices. Furthermore, an exciplex-forming cohost strategy is adopted. The devices achieve a record EQE of 28.1% and a deep-red EL peak at 648 nm with the CIE coordinates of (0.66, 0.34). Last, nondoped devices exhibit 5.3% EQE and an NIR EL peak at 680 nm with the CIE coordinates of (0.69, 0.30).

9,9'-Bicarbazole: New Molecular Skeleton for Organic Light-Emitting Diodes.

Carbazole is a classic tricyclic aromatic compound that has been widely used in organic optoelectronics. Appropriate functionalization on its aromatic rings will significantly increase the possibilities for its application as an optoelectronic material. Position engineering of carbazole not only leads to its structural diversity, but also substantially enriches its functionality. Bicarbazoles have 15 isomers, most of which are well studied and have been applied in organic light-emitting diodes (OLEDs). However, one isomer, 9,9'-bicarbazole, is rarely investigated as an OLED material. Therefore, two 9,9'-bicarbazole derivatives, 3,3'-di(10H-phenoxazin-10-yl)-9,9'-bicarbazole and 3,3'-di(10H-phenothiazin-10-yl)-9,9'-bicarbazole, have been designed and prepared for use as host materials for green and red OLEDs. These two compounds demonstrated good device performances, and it is believed that the 9,9'-bicarbazole building block could be a novel platform for the design of efficient host materials for OLEDs.