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Multi‐resonance (MR) type emitters have emerged as highly promising candidates for high‐resolution organic light‐emitting diodes (OLEDs). However, thermally activated delayed fluorescence (TADF) emissions with simultaneous short excited state lifetimes and ultrapure blue color (a CIEy close to 0.046 and an emission peak >440 nm) have rarely been obtained for MR emitters. Herein, we report a design of dual gold‐coordinated MR molecules to achieve efficient and short‐lived ultrapure blue TADF emission. The dinuclear Au(I) complex, namely iPrAuBN, shows a narrowband deep‐blue emission with a peak maximum of 448 nm and a full width at half maximum (FWHM) of 29 nm in doped film. The coordination with two Au atoms significantly shortens the delayed fluorescence lifetime to 7.8 μs in comparison to 60.6 μs for the parental organic analogue. Solution‐processed OLED doped with iPrAuBN demonstrates an ultrapure blue electroluminescence with a peak maximum of 442 nm, a FWHM of 19 nm, CIE coordinates of (0.154, 0.036), and a maximum external quantum efficiency of 14.8 %. [ABSTRACT FROM AUTHOR]

Two‐coordinate Au(I) complexes with a donor‐metal‐acceptor (D‐M‐A) structure have shown rich luminescent properties. However, charge‐neutral dinuclear donor‐metal‐acceptor type Au(I) complexes featuring aurophilic interactions have been seldom explored. Herein, we describe the structures and photoluminescence properties of two dinuclear Au(I) complexes, namely DiAu‐Ph and DiAu‐Me. Single crystal X‐ray structural analysis of DiAu‐Ph reveals a short intramolecular Au‐Au distance of 3.224 Å. In dilute solution and doped films, excitation wavelength dependent multiple phosphorescence phenomena were observed for these dinuclear complexes. Theoretical calculations reveal that the aurophilic interaction causes increased contribution of the Au d orbital to the highest occupied molecular orbitals. Thus, the gap between singlet and triplet excited states (ΔEST) is enlarged, which disables the thermally activated delayed fluorescence (TADF). Moreover, the large energy separation (0.45–0.52 eV) and the different orbital configurations between the various excited states result in an inefficient internal conversion, accounting for their multiple phosphorescence properties. [ABSTRACT FROM AUTHOR]

A new class of carbene–anilido boron complexes have been designed and synthesized. The complexes show intense fluorescence with large Stokes shift because of their charge-transfer excited states, different from typical BODIPY dyes. By using a chiral 1,1′-bi(2-naphthol) ligand, dyes exhibiting circularly polarized luminescence can also be facilely developed. [ABSTRACT FROM AUTHOR]

The second‐row transition metal complexes have been much less exploited as emitters for organic light‐emitting diodes (OLEDs). Despite the considerable efforts to develop phosphorescent Pd(II) complexes by ligand design, the triplet excited states of Pd(II) complexes usually have very long lifetimes because of their ligand‐centered nature. Hereina panel of sandwich‐type mononuclear Pd(II) complexes is reported, namely PdDDBPZ, PdDTRZ, and PdDPYR, which exhibit strong yellow to red thermally activated delayed fluorescence (TADF) with photoluminescence quantum yields (PLQYs) of 87–94% in doped films. The metal ion plays a perturbing role in the intraligand charge transfer excited state dynamics, giving rise to accelerated reverse intersystem crossing (RISC). Owing to the space‐confined sandwich configuration, there are multiple noncovalent interactions within the molecules, which are qualitatively and quantitatively analyzed by theoretical calculations. The Pd(II) complexes show high device efficiencies with external quantum efficiencies (EQEs) up to 31.5%. The ultralow efficiency roll‐off is as low as 1% at 1000 cd m−2. The device operational stability test for PdDTRZ reveals a half‐lifetime (LT50) of 1615 h at an initial luminance of 3000 cd m−2. The leverage of metal‐promoted TADF mechanism together with intramolecular noncovalent interactions proves feasible for developing practical Pd(II)‐TADF emitters toward OLEDs. [ABSTRACT FROM AUTHOR]

The second‐row transition metal complexes have been much less exploited as emitters for organic light‐emitting diodes (OLEDs). Despite the considerable efforts to develop phosphorescent Pd(II) complexes by ligand design, the triplet excited states of Pd(II) complexes usually have very long lifetimes because of their ligand‐centered nature. Hereina panel of sandwich‐type mononuclear Pd(II) complexes is reported, namely PdDDBPZ, PdDTRZ, and PdDPYR, which exhibit strong yellow to red thermally activated delayed fluorescence (TADF) with photoluminescence quantum yields (PLQYs) of 87–94% in doped films. The metal ion plays a perturbing role in the intraligand charge transfer excited state dynamics, giving rise to accelerated reverse intersystem crossing (RISC). Owing to the space‐confined sandwich configuration, there are multiple noncovalent interactions within the molecules, which are qualitatively and quantitatively analyzed by theoretical calculations. The Pd(II) complexes show high device efficiencies with external quantum efficiencies (EQEs) up to 31.5%. The ultralow efficiency roll‐off is as low as 1% at 1000 cd m−2. The device operational stability test for PdDTRZ reveals a half‐lifetime (LT50) of 1615 h at an initial luminance of 3000 cd m−2. The leverage of metal‐promoted TADF mechanism together with intramolecular noncovalent interactions proves feasible for developing practical Pd(II)‐TADF emitters toward OLEDs. [ABSTRACT FROM AUTHOR]

Two‐coordinate coinage metal complexes have been exploited for various applications. Herein, a new donor‐metal‐acceptor (D–M–A) complex PZI‐Au‐TOT, using bulky pyrazine‐fused N‐heterocyclic carbene (PZI) and trioxytriphenylamine (TOT) ligands, was synthesized. PZI‐Au‐TOT displays decent thermally activated delayed fluorescence (TADF) with a quantum yield of 93 % in doped film. The crystals of PZI‐Au‐TOT show simultaneous TADF, polymorphism, and linearly polarized luminescence (LPL). The polymorph‐dependent emission properties with widely varied peaks from 560 to 655 nm are attributed to different packing modes in terms of isolated monomers, discrete π–π stacked dimers or dimer PLUS. Two well‐defined microcrystals of PZI‐Au‐TOT exhibit linearly polarized thermally activated delayed fluorescence with a degree of polarization up to 0.64. This work demonstrates that the molecular rotational flexibility of D–M–A type complexes endows an integration of multiple functions into one complex through manipulation of supramolecular aggregation. This type of complexes is expected to serve as a versatile platform for the fabrication of crystal materials for advanced photonic applications. [ABSTRACT FROM AUTHOR]

Although phosphorescent Pt(II) complexes have shown great potential for organic light-emitting diodes (OLEDs), red phosphorescence with a high photoluminescence quantum yield (PLQY) and a short emission lifetime is still scarce because of the limitation on the radiative decay rate. Transition metal complexes have proved advantageous for emitting thermally activated delayed fluorescence (TADF), but TADF Pt(II) complexes have rarely been reported. Herein, we describe the design and synthesis of two red TADF Pt(II) complexes, namely Pt-tCzDBPZ (Pt1) and Pt2-tCzDBPZ (Pt2). By using a donor–acceptor type monodentate ligand, the complexes have metal-perturbed intraligand charge-transfer (MPICT) excited states featuring small singlet–triplet energy gaps (0.086–0.089 eV) and a moderately large spin–orbit coupling matrix element (∼10 cm−1). The complexes exhibit red TADF emissions (ca. 630 nm) with high PLQYs of 82–92% and delayed fluorescence lifetimes of 1.51–1.63 μs. The vacuum-deposited red OLEDs based on Pt-tCzDBPZ show high external quantum efficiencies of up to 35.6% and small roll-offs. In spite of the significant heavy atom effect of Pt for facilitating phosphorescence, this study demonstrates a feasible design of Pt(II)–TADF emitters which can enable them to outperform phosphorescent Pt(II) complexes. [ABSTRACT FROM AUTHOR]

B‐ and N‐embedded multiple resonance (MR) type thermally activated delayed fluorescence (TADF) emitters usually suffer from slow reverse intersystem crossing (RISC) process and aggregation‐caused emission quenching. Here, we report the design of a sandwich structure by placing the B−N MR core between two electron‐donating moieties, inducing through‐space charge transfer (TSCT) states. The proper adjusting of the energy levels brings about a 10‐fold higher RISC rate in comparison with the parent B−N molecule. In the meantime, a high photoluminescence quantum yield of 91 % and a good color purity were maintained. Organic light‐emitting diodes based on the new MR emitter achieved a maximum external quantum efficiency of 31.7 % and small roll‐offs at high brightness. High device efficiencies were also obtained for a wide range of doping concentrations of up to 20 wt % thanks to the steric shielding of the B−N core. A good operational stability with LT95 of 85.2 h has also been revealed. The dual steric and electronic effects resulting from the introduction of a TSCT state offer an effective molecular design to address the critical challenges of MR‐TADF emitters. [ABSTRACT FROM AUTHOR]

Three-coordinate Au(I) complexes with thermally activated delayed fluorescence (TADF) have recently gained experimental attention. However, its luminescence mechanism is elusive. Herein, we have employed density functional theory (DFT), time-dependent DFT (TD-DFT), and QM/MM methods to investigate the excited-state and emission properties of the Au(I) complex in both gas and crystal phases. In both environments, the S1 and T1 emitting states mainly involve HOMO and LUMO and show clear metal-ligand charge transfer and intraligand charge transfer characters. The good spatial separation of HOMO and LUMO minimizes the S1–T1 energy gap, which benefits the reverse intersystem crossing (rISC) from T1 to S1. At 300 K, the rISC rate is faster than the T1 phosphorescence emission, which enables the TADF emission. However, at 77 K, such a rISC process is blocked and TADF disappears; instead, only phosphorescence is recorded experimentally. Importantly, this work highlights the importance of environments in regulating luminescence properties and contributes to understanding the TADF emission of organometallic complexes. [ABSTRACT FROM AUTHOR]

Although two‐coordinate Cu(I) complexes are highly promising low‐cost emitters for organic light‐emitting diodes (OLEDs), the exposed metal center in the linear coordination geometry makes them suffer from poor stability. Herein, we describe a strategy to develop stable carbene‐Cu‐amide complexes through installing intramolecular noncovalent Cu⋅⋅⋅H interactions. The employment of 13H‐dibenzo[a,i]carbazole (DBC) as the amide ligand leads to short Cu⋅⋅⋅H distances in addition to the Cu−N coordination bond. The resultant Cu(I) complexes exhibit yellow thermally activated delayed fluorescence with photoluminescence quantum yields of up to 86 % and radiative decay rate constants on the order of 106 s−1. Comparing with the analogues without Cu⋅⋅⋅H interactions, the pincer complexes have significantly improved stability. The vacuum‐deposited OLEDs show high‐performance electroluminescence with maximum external quantum efficiencies of up to 29.5 % and extremely small roll‐offs of only 3.5 % at 10,000 cd m−2. Remarkably, the operational lifetimes (LT90) are up to 68 h with an initial luminance of 3000 cd m−2. This work proves a feasible design of robust low‐coordinate metal complexes by leveraging secondary coordination interactions, which helps to overcome the long‐standing stability problem. [ABSTRACT FROM AUTHOR]

Transition metal complexes exhibiting thermally activated delayed fluorescence (TADF) remain underdeveloped for organic light-emitting diodes (OLEDs). Here, we describe a design of TADF Pd(II) complexes featuring metal-perturbed intraligand charge-transfer excited states. Two orange- and red-emitting complexes with efficiencies of 82 and 89% and lifetimes of 2.19 and 0.97 μs have been developed. Combined transient spectroscopic and theoretical studies on one complex reveal a metal-perturbed fast intersystem crossing process. OLEDs using the Pd(II) complexes show maximum external quantum efficiencies of 27.5 to 31.4% and small roll-offs down to 1% at 1000 cd m -2 . Moreover, the Pd(II) complexes show exceptional operational stability with LT 95 values over 220 hours at 1000 cd m -2 , benefiting from the use of strong σ-donating ligands and the presence of multiple intramolecular noncovalent interactions beside their short emission lifetimes. This study demonstrates a promising approach for developing efficient and robust luminescent complexes without using the third-row transition metals.

We synthesized the scientific research carried out in Changbai Mountain from 1956 to 2018 by mapping knowledge domains and bibliometrics based on the literature from international database (WOS) and domestic databases (CNKI and CSCD). The results showed that natural science research in Changbai Mountain underwent three stages during 1956-2018, including embryo stage, growing stage, and rapid development stage. The natural research in Changbai Mountain could be divided into five fields, i.e., forest and ecological science, volcano and geology science, environmental change science, resource sciences and utilization, animal and microbial science, with a total of 20 main research directions. Since 2000, forest and ecological science, volcano and geological science, environmental change science dominated the natural science research in Changbai Mountain. The researches in recent 20 years mainly concentrated on the following seven disciplines: community ecology, forest management, soil ecology, ecosystem ecology, eco-climatology, forest responses to environmental change, and volcanic geology. International researches showed a trend of strong integration of different disciplines. We forecast that the natural science research in the Changbai Mountain would deepen its research in the next decade. Moreover, other fields such as old-growth forest and large-scale ecosystem carbon processes, forest-altitude-climate change, soil fauna and microorganisms, forest management and human activities, biodiversity, volcanic origin and eruption history, volcanic eruption dynamics and volcanic monitoring will emerge as the new research focus. Scale polarization, elements diversification, discipline crossing, and research deepening would be the future trend of natural science research in Changbai Mountain.