Search

AbstractIn the area of big data, hierarchical time series prediction (HTSP) has attracted extensive attention. For the traditional HTSPs, the uncertainty of model selection cannot be alleviated due to the shortcomings of data information loss. This article proposes a new HTSP method based on the adjustable error to deal with the above issue. Detailly speaking, in the essential prediction stage, the adjustable prediction error, including all data information, is introduced to improve the current prediction. By comparison of four cases of optimal single prediction, optimal combined prediction, optimal single prediction under the new method, and optimal combined prediction under the new method, the two assertions are obtained: (1) the prediction accuracy of this new method is significantly improved compared with the widely used methods such as bottom-up, generalized least squares; (2) the uncertainty of model selection is greatly reduced. The method’s validity is verified by the examples of American clothing retail and the Germany national electricity consumption. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence emitters with multiple resonance effect have drawn much attention very recently for their extremely sharp spectra and nearly unity photoluminescence quantum yields, showing promising potential for application in ultra-high-definition displays and organic light-emitting diodes. Though strategies have been put forward for tuning the emitting color of these molecules, most emitters have been faced with the problem of spectral broadening once the emission is redshifted. Herein, by virtue of the increased short-range charge transfer advantages of 5-phenyl-5,7-dihydroindolo[2,3-b]carbazole, an asymmetrical B, N/O based MR emitter (IDCzBNO) is constructed. Compared with its carbazole containing predecessor, IDCzBNO shows bathochromic-shifted spectra, from deep blue to blue emission without sacrificing color purity. And the emitter exhibited bright blue emission peaking at 458 nm with a full-width-at-half-maximum of 24 nm in solution, as well as a high fluorescence quantum efficiency of 95%. Besides, thanks to its more expanded planar structure, a high horizontal emitting dipole orientation of 83% is obtained in doped films. As a result, the related blue OLED devices employing the triplet–triplet annihilation mechanism exhibited a small FWHM of 28 nm and the maximum external quantum efficiency of 11.5% with negligible efficiency roll-off, manifesting the effectiveness of the red-shifting emission spectra in achieving ideal narrowband blue emitters. [ABSTRACT FROM AUTHOR]

A fast reverse intersystem crossing (RISC) remains an ongoing pursuit for multiresonance (MR) emitters but faces formidable challenges, particularly for indolocarbazole (ICz) derived ones. Here, heavy-atom effect is introduced first to construct ICz-MR emitter using a sulfur-containing substitute, simultaneously enhancing both spin-orbit and spin-vibronic coupling to afford a fast RISC with a rate of 1.2 × 10 5  s -1 , nearly one order of magnitude higher than previous maximum values. The emitter also exhibits an extremely narrow deep-blue emission peaking at 456 nm with full-width at half-maxima of merely 12 nm and a photoluminescence quantum yield of 92%. Benefiting from its efficient triplet upconversion capability, this emitter achieves not only a high maximum external quantum efficiency (EQE) of 31.1% in organic light-emitting diodes but also greatly alleviates efficiency roll-off, affording record-high EQEs of 29.9% at 1000 cd m -2 and 18.7% at 5000 cd m -2 among devices with ICz-MR emitters., (© 2024 Wiley‐VCH GmbH.)

Extending the π-skeletons of multi-resonance (MR) organoboron emitters can feasibly modulate their optoelectronic properties. Here, we first adopt the indolo[3,2-b]indole (32bID) segment as a multi-nitrogen bridge and develop a high-efficiency π-extended narrowband green emitter. This moiety establishes not only a high-yield one-shot multiple Bora-Friedel-Crafts reaction towards a π-extended MR skeleton, but a compact N-ethylene-N motif for a red-shifted narrowband emission. An emission peak at 524 nm, a small full width at half maximum of 25 nm and a high photoluminescence quantum yield of 96 % are concurrently obtained in dilute toluene. The extended molecular plane also results in a large horizontal emitting dipole orientation ratio of 87 %. A maximum external quantum efficiency (EQE) of 36.6 % and a maximum power efficiency of 135.2 lm/W are thereafter recorded for the corresponding device, also allowing a low efficiency roll-off with EQEs of 34.5 % and 28.1 % at luminance of 1,000 cd/m 2 and 10,000 cd/m 2 , respectively., (© 2023 Wiley-VCH GmbH.)

Though the flourishment of materials with multiple resonance (MR) in blue to green regions, red-emissive MR emitters are still rare in literatures, which definitely should be resolved for further applications. Herein, we report a simple molecular design strategy for the construction of pure-red MR emitters by conjugate charge transfer, which could greatly enhance the π-conjugation degree and charge-transfer property of the target molecule while maintaining the basic feature of MR, leading to a significant redshift of more than 128 nm compared to the selected parent MR core. The proof-of-concept emitter PPZ-BN exhibited a pure-red emission with a dominant peak at 613 nm and a small full-width-at-half-maximum of 0.16 eV (48 nm). The optimized organic light-emitting diode showed a high external quantum efficiency of 26.9 %, a small efficiency roll-off, and an excellent operation stability (LT99) of more than 43 hours at an initial luminance of 10 000 cd m -2 ., (© 2023 Wiley-VCH GmbH.)

A novel macrocycle of B/N-doped calix[4]arene (C-BN) was synthesized by a one-shot double boronation. Owing to the structural tension and electron-donating properties of the nitrogen atoms in the macrocycle, reaction selectively proceeds between the adjacent benzene rings outside the macrocycle. C-BN shows a highly centrosymmetric structure with two multiple resonance (MR) fragments bridged by tertiary amine groups at the 1,3 positions of the benzene ring. Benefiting from the large intermolecular distance (>4.6 Å) between adjacent MR-emitting cores, C-BN also exhibits excellent narrowband emitting features against aggregation-induced quenching and spectrum broadening. Optimized organic light-emitting diode devices based on C-BN exhibit high maximum external quantum efficiencies of 24.7-26.6 % and small full width at half maximums of 25-28 nm over a wide doping range of 1-12 wt %., (© 2022 Wiley-VCH GmbH.)

Boron- and nitrogen (BN)-fused polycyclic aromatic frameworks with amine-directed formation of B-N covalent bonds have the potential to form a new family of facile-synthesis multi-resonance luminophores, which, however, still face imperative challenges in diversifying the molecular design to narrow the emission bandwidth and tune the emission colors. Here, we demonstrate a strategic implementation of B-N bond containing polycyclo-heteraborin multi-resonance emitters with wide-range colors from deep-blue to yellow-green (442-552 nm), small full-width at half-maxima of only 19-28 nm and high photoluminescence efficiencies, by stepwise modifying the basic para B-π-B structures with heteroatoms. The corresponding electroluminescent devices show superior maximum external quantum efficiencies with an exceptional low-efficiency roll-off, retaining 21.0%, 23.6% and 22.1% for the sky-blue, green and yellow-green devices at a high luminance of 5000 cd m -2 , respectively., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Narrowband, full-color, and quenching-resistant emitters are urgently needed for the next generation high-resolution displays. Though the flourishment of narrowband multiple resonance (MR) emitters in blue region, these materials still face thorny challenges such as effective light-color regulation strategies and concentration-induced spectral broadening/emission quenching. Herein, the research status of an effective "decoration strategy for para B position" is highlighted. On one hand, the introduction of an electron donor or acceptor could induce a hypsochromic- or bathochromic-shift emission, respectively, without undesirable FWHM broadening. On the other hand, a more advanced molecular motif is further proposed through adopting a peripheral benzene ring on the para position of the B-substituted phenyl in MR core to construct the high-purity, high-efficiency, quenching-resistant and stable MR emitters. Such concept is expected to provide a possible way for the modification, optimization and expansion of MR emitters to meet more possible applications., (© 2022 Wiley-VCH GmbH.)