In this study, we synthesized and characterized multiple resonance (MR) type blue thermally activated delayed fluorescence (TADF) emitters. Unlike many boron-based MR-TADF materials, the blue TADF emitters of this work had an asymmetric molecular structure with one boron, one oxygen, and one nitrogen. The aromatic units linked to the nitrogen were changed into diphenylamine, carbazole, dimethylacridine, and diphenylacridine to manage the light emission properties of the emitters. The TADF emitters exhibited a blue emission due to the weak electron-donating oxygen atom and the emission color was controlled by the aromatic unit connected to the nitrogen. The simple diphenylamine unit was effective in achieving real deepblue emission for the BT2020 standard with a high external quantum efficiency (EQE), while the electron-rich nitrogen-based dimethylacridine and diphenylacridine accelerated the reverse intersystem crossing for high EQE and small EQE roll-off. Among the emitters, a diphenylamine-substituted emitter, 7-(tert-butyl)-9-phenyl-9H-5-oxa-9-aza-13b-boranaphtho-[3,2,1-de]anthracene (B-O-dpa), showed a maximum external quantum efficiency of 16.3%, a small full width at half-maximum of 32 nm, and a real deep-blue color coordinate of (0.15, 0.05).

A novel violet emitter, 1,3-bis [10,10-dimethyl-10H-indeno[2,1-b]]indolo[3,2,1jk]indolo[1′,2′,3′:1,7]indolo[3,2-b]carbazole (m-FLDID), was designed and synthesized by meta-oriented bis-fusion of two 7,7-dimethyl-5,7-dihydroindeno[2,1-b]carbazole (DMID) subunits for use in a pure violet organic light-emitting diode (OLED). Incorporation of the DMID subunits effectively reduced the nonradiative recombination rate, improving the photoluminescence quantum yield of the m-FLDID emitter. The meta-oriented bis-fusion of the two DMID subunits not only triggered an alternative distribution of the frontier orbitals but also effectively locked the π-conjugation chain, which ultimately resulted in a narrow-band, pure violet emission of the m-FLDID emitter. Doped m-FLDID devices possessed an external quantum efficiency (EQE) of > 5%, pure violet emission with a maximum at 407 nm, a narrow full width at half-maximum of 17 nm, and a Commission Internationale de l'ećlairage y coordinate of less than 0.03. This is the first work reporting an EQE of > 5% and an extremely narrow emission spectrum for a pure violet emitter.

Realizing high efficiency deep blue emission with a Commission international de I'Eclairage (CIE) coordinate of CIEy < 0.08 is still a big challenge. In this contribution, three molecules, named TTT‐TPA‐R (R = H, OMe, tBu), using tris(triazolo)triazine (TTT) as the acceptor and triphenylamine derivatives (TPA‐R, R = H, OMe, and tBu) as the donor are prepared and characterized. All these emitters show deep/pure blue emission between 420 and 470 nm in the PMMA film, concomitant with the excellent emission efficiency of 80–100%. Both experimental and calculated methods demonstrate that these emitters exhibit a clearly hybridized local and charge‐transfer excited state and can harvest both singlet and triplet excitons via reverse intersystem crossing process from the high‐lying triplet to singlet states. Therefore, the solution processable deep blue organic light‐emitting diodes (OLEDs) achieve a maximum external quantum efficiency (EQEmax) of 10.5% which is the recorded value for the solution processable deep blue OLED based on the “hot exciton” mechanism. Using TTT‐TPA‐H as the host material, solution‐processed phosphorescent OLED based on PO‐01 presents the EQEmax of 20.2%. These results pave a novel avenue for designing highly efficient deep blue emitter in solution processable OLED.

To realize transparent organic light-emitting diodes (OLEDs), a top electrode should have excellent optical, electrical, and mechanical properties. Conventionally, transparent conductive oxides and semitransparent metal have been widely used for transparent top electrodes, but they have several fundamental drawbacks. We herein report efficient large-area inverted transparent OLEDs using a vacuumlaminated top electrode with an embedded metal mesh. The laminated device with 1 mm pitch exhibits superior optical properties including a high transmittance of 75.9% at 550 nm, a low reflectance of 12.0% at 550 nm, and spectrally flat characteristics over the entire visible region and shows nearly ideal Lambertian angular emission characteristics with little angular color shift in both directions. Moreover, the lowered sheet resistance of 4 Ω/sq originating from the embedded metal mesh (1 mm pitch) led to efficient and uniform emission characteristics. As a result, the device shows a relatively high maximum current efficiency of 50.3 cd/A (bottom: 24.5 cd/A; top: 25.8 cd/A) and a maximum external quantum efficiency of 15.3% (bottom: 7.9%; top: 7.4%), which surpasses all previously reported values based on a laminated top electrode. In addition, we successfully demonstrate its potential as a large-area transparent top electrode in various optoelectronic devices through a large-area transparent OLED segment panel (45 × 90 mm 2 , diagonal length of 70.2 mm in the active area) with a laminated top electrode.

Perovskite-type Nd 1-x Sr x CoO 3-y catalysts with various Sr mole fraction were prepared and investigated for the effect of Sr substitution on their catalytic activities in the oxidation of carbon monoxide. Utilizing the static and flow methods, kinetic studies have been carried out between 373 and 523 K. The initial reaction was investigated by the static reactor system using a differential photoacoustic cell, and for the study of reaction stage showing a constant catalytic activity after an initial stage characterized by high reaction rates, the flow reactor system using on-line gas chromatography was employed. The catalytic activity increased with increasing amounts of Sr substitution for Nd in NdCoO 3 compounds, and it also increased with higher reaction temperature within the range of 373-523 K. Kinetic data obtained in an initial reaction stage by CO 2 photoacoustic spectroscopy showed that the reaction partial orders to CO and O 2 were 0.8-0.9 and 0, respectively. In the reaction stage showing a constant catalytic activity after an initial stage, the oxidation was found to be first order with respect to CO and 0.5 order with respect to O 2 . The concentration of oxygen vacancy in the solid catalyst was shown to be the controlling factor for the oxidation of carbon monoxide. According to the experimental results, the mechanisms of the CO oxidation processes are discussed, and it is believed that O 2 adsorbs on the oxygen vacancies (V o x ) formed by Sr substitution while CO adsorbs on the lattice oxygens during the reaction process.