Intramolecular through‐space charge‐transfer (TSCT) excited states have been exploited for developing thermally activated delayed fluorescence (TADF) emitters, but the tuning of excited state ...dynamics by conformational engineering remains sparse. Designed here is a series of TSCT emitters with precisely controlled alignment of the donor and acceptor segments. With increasing intramolecular π–π interactions, the radiative decay rate of the lowest singlet excited state (S1) progressively increased together with a suppression of nonradiative decay, leading to significantly enhanced photoluminescence quantum yields of up to 0.99 in doped thin films. A high‐efficiency electroluminescence device, with a maximum external quantum efficiency (EQE) of 23.96 %, was achieved and maintains >20 % at a brightness of 1000 cd m−2. This work sheds light on the importance of conformation control for achieving high‐efficiency intramolecular exciplex emitters.
The orientations of donor and acceptor have been controlled for the development of thermally activated delayed fluorescence emitters featuring intramolecular through‐space charge‐transfer excited states. With maximized cofacial π–π interactions between the quasiplanar donor and acceptor segments, a substantial enhancement of radiative decay rate together with a suppressed nonradiative decay resulted in an emission efficiency of almost unity.
A new series of tetrahedral heteroleptic copper(I) complexes exhibiting efficient thermally-activated delayed fluorescence (TADF) in green to orange electromagnetic spectral regions has been ...developed by using D-A type N^N ligand and P^P ligands. Their structures, electrochemical, photophysical, and electroluminescence properties have been characterized. The complexes exhibit high photoluminescence quantum yields (PLQYs) of up to 0.71 at room temperature in doped film and the lifetimes are in a wide range of 4.3-24.1 μs. Density functional theory (DFT) calculations on the complexes reveal the lowest-lying intraligand charge-transfer excited states that are localized on the N^N ligands. Solution-processed organic light emitting diodes (OLEDs) based on one of the new emitters show a maximum external quantum efficiency (EQE) of 7.96%.
Luminescent coinage metal complexes have shown promising applications as electroluminescent emitters, photocatalysts/photosensitizers, and bioimaging/theranostic agents, rendering them attractive ...alternatives to transition metal complexes based on iridium, ruthenium, and platinum that have extremely low earth abundance. In comparison to the widely studied Au(I) and Cu(I) complexes, Ag(I) complexes have seldom been explored in this field because of their inferior emission properties. Herein, we report a novel series of Ag(N^N)(P^P)PF6 complexes exhibiting highly efficient thermally activated delayed fluorescence by using easily accessible neutral diamine ligands and commercially available ancillary diphosphine chelates. The photoluminescence quantum yields (PLQYs) of the Ag(I) emitters are ≤0.62 in doped films. The high PLQY with a large delayed fluorescence ratio enabled the fabrication of solution-processed organic light-emitting diodes (OLEDs) with a high maximum external quantum efficiency of 8.76%, among the highest values for Ag(I) emitter-based OLEDs. With superior emission properties and an excited state lifetime in the microsecond regime, together with its potent cytotoxicity, the selected Ag(I) complex has been used for simultaneous cell imaging and anticancer treatment in human liver carcinoma HepG2 cells, revealing the potential of luminescent Ag(I) complexes for biological applications such as theranostics.
ZnII complexes exhibiting strong emission in the solid state remain scarce, and most of them exhibit only prompt fluorescence. Herein the synthesis, structures, and photoluminescence properties of ...two ZnII complexes containing new donor–acceptor ligands is reported. The new ZnII complexes have dinuclear structures in which each metal ion adopts a distorted square‐pyramidal geometry. The ZnII complexes show strong emission in the solid state with quantum yields up to 50 %. Variable‐temperature transient photoluminescence studies revealed an emission mechanism involving prompt and thermally activated delayed fluorescence (TADF). DFT calculations showed well‐separated HOMO and LUMO in the ground state and small excited singlet–triplet energy splitting, accounting for the TADF. The complexes also exhibit different emission colors in the as‐synthesized powder state and in single crystals, that is, they exhibit luminescence polymorphism. The single‐crystal emission is responsive to mechanical grinding and was characterized by powder XRD.
Now and later: Two new dinuclear ZnII complexes containing donor–acceptor‐type ligands were structurally characterized and their photoluminescent properties examined. The ZnII complexes luminesce strongly in the solid state by prompt and thermally activated delayed fluorescence (TADF) with emission quantum yields up to 50 %. The complexes also exhibit luminescence polymorphism that is responsive to mechanical stimulus.
A molecular design to high‐performance red and near‐infrared (NIR) organic light‐emitting diodes (OLEDs) emitters remains demanding. Herein a series of dinuclear platinum(II) complexes featuring ...strong intramolecular Pt⋅⋅⋅Pt and π–π interactions has been developed by using N‐deprotonated α‐carboline as a bridging ligand. The complexes in doped thin films exhibit efficient red to NIR emission from short‐lived (τ=0.9–2.1 μs) triplet metal‐metal‐to‐ligand charge transfer (3MMLCT) excited states. Red OLEDs demonstrate high maximum external quantum efficiencies (EQEs) of up to 23.3 % among the best PtII‐complex‐doped devices. The maximum EQE of 15.0 % and radiance of 285 W sr−1 m−2 for NIR OLEDs (λEL=725 nm) are unprecedented for devices based on discrete molecular emitters. Both red and NIR devices show very small efficiency roll‐off at high brightness. Appealing operational lifetimes have also been revealed for the devices. This work sheds light on the potential of intramolecular metallophilicity for long‐wavelength molecular emitters and electroluminescence.
Strong intramolecular Pt⋅⋅⋅Pt/π–π interactions confined by rigid bridges lead to fast radiative decay and high‐efficiency red and near‐infrared (NIR) phosphorescence from triplet metal‐metal‐to‐ligand charge transfer (3MMLCT) excited states. Together with short emission lifetimes, high‐performance red and NIR organic light‐emitting diodes (OLEDs) have been demonstrated.
Intramolecular through‐space charge‐transfer (TSCT) excited states have been exploited for developing thermally activated delayed fluorescence (TADF) emitters, but the tuning of excited state ...dynamics by conformational engineering remains sparse. Designed here is a series of TSCT emitters with precisely controlled alignment of the donor and acceptor segments. With increasing intramolecular π–π interactions, the radiative decay rate of the lowest singlet excited state (S1) progressively increased together with a suppression of nonradiative decay, leading to significantly enhanced photoluminescence quantum yields of up to 0.99 in doped thin films. A high‐efficiency electroluminescence device, with a maximum external quantum efficiency (EQE) of 23.96 %, was achieved and maintains >20 % at a brightness of 1000 cd m−2. This work sheds light on the importance of conformation control for achieving high‐efficiency intramolecular exciplex emitters.
The orientations of donor and acceptor have been controlled for the development of thermally activated delayed fluorescence emitters featuring intramolecular through‐space charge‐transfer excited states. With maximized cofacial π–π interactions between the quasiplanar donor and acceptor segments, a substantial enhancement of radiative decay rate together with a suppressed nonradiative decay resulted in an emission efficiency of almost unity.
Zn
complexes exhibiting strong emission in the solid state remain scarce, and most of them exhibit only prompt fluorescence. Herein the synthesis, structures, and photoluminescence properties of two ...Zn
complexes containing new donor-acceptor ligands is reported. The new Zn
complexes have dinuclear structures in which each metal ion adopts a distorted square-pyramidal geometry. The Zn
complexes show strong emission in the solid state with quantum yields up to 50 %. Variable-temperature transient photoluminescence studies revealed an emission mechanism involving prompt and thermally activated delayed fluorescence (TADF). DFT calculations showed well-separated HOMO and LUMO in the ground state and small excited singlet-triplet energy splitting, accounting for the TADF. The complexes also exhibit different emission colors in the as-synthesized powder state and in single crystals, that is, they exhibit luminescence polymorphism. The single-crystal emission is responsive to mechanical grinding and was characterized by powder XRD.
Adipic acid (AA) is a crucial feedstock for nylon polymers, and is industrially produced by thermal oxidation of cyclohexanone/cyclohexanol mixture (KA oil). However, this process consumes large ...quantities of corrosive nitric acid as oxidants, while emits ozone‐depleting greenhouse gas N2O. Here, an electrocatalytic strategy for selective oxidation of KA oil to AA coupled with H2 evolution over a Co3O4/graphdiyne cooperative catalyst (Co3O4/GDY) is reported. The Co3O4/GDY displays high electrooxidation activity of KA oil to AA (100 mA cm−2 at ≈1.5 V vs RHE), outperforming all the reported findings. Detailed ex situ and in situ experimental studies, theoretical calculations, and molecular dynamic simulations reveal that GDY not only facilitates the enrichment of cyclohexanone on the catalyst surface in aqueous medium, but also upshifts the d‐band center of Co sites, strengthening the adsorption/activation of cyclohexanone. This study offers a green route for AA synthesis and proposes a GDY interface engineering strategy for efficient electrooxidation.
Highly efficient electrooxidation of cyclohexanone/cyclohexanol mixture (KA oil) into adipic acid coupled with H2 evolution is achieved over a Co3O4/graphdiyne cooperative catalyst (Co3O4/GDY). GDY, as an electron modifier, can upshift the d‐band center of Co3O4, which facilitates the enrichment, adsorption, and activation of cyclohexanone on the catalyst surface in aqueous solutions, resulting in top‐level activity (100 mA cm−2 at ≈1.5 V vs RHE) and high yield of AA (>82%).
A molecular design to high‐performance red and near‐infrared (NIR) organic light‐emitting diodes (OLEDs) emitters remains demanding. Herein a series of dinuclear platinum(II) complexes featuring ...strong intramolecular Pt⋅⋅⋅Pt and π–π interactions has been developed by using N‐deprotonated α‐carboline as a bridging ligand. The complexes in doped thin films exhibit efficient red to NIR emission from short‐lived (τ=0.9–2.1 μs) triplet metal‐metal‐to‐ligand charge transfer (3MMLCT) excited states. Red OLEDs demonstrate high maximum external quantum efficiencies (EQEs) of up to 23.3 % among the best PtII‐complex‐doped devices. The maximum EQE of 15.0 % and radiance of 285 W sr−1 m−2 for NIR OLEDs (λEL=725 nm) are unprecedented for devices based on discrete molecular emitters. Both red and NIR devices show very small efficiency roll‐off at high brightness. Appealing operational lifetimes have also been revealed for the devices. This work sheds light on the potential of intramolecular metallophilicity for long‐wavelength molecular emitters and electroluminescence.
Strong intramolecular Pt⋅⋅⋅Pt/π–π interactions confined by rigid bridges lead to fast radiative decay and high‐efficiency red and near‐infrared (NIR) phosphorescence from triplet metal‐metal‐to‐ligand charge transfer (3MMLCT) excited states. Together with short emission lifetimes, high‐performance red and NIR organic light‐emitting diodes (OLEDs) have been demonstrated.
We document issuance overpricing of corporate debt securities in China, which is robust across subsamples with different credit ratings, maturities, and issuers. This phenomenon contrasts with ...underpricing of equity and debt securities in Western countries and reflects China's distinct institutional environment. The average overpricing dropped from 7.44 basis points to 2.41 basis points after the government prohibited underwriters from using rebates in issuances in October 2017. By analyzing overpricing before and after the rebate ban and across different issuers and underwriters, we uncover two channels for underwriters, who compete for future underwriting business, to drive up overpricing: rebates and self-purchases.
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