Organic Light‐Emitting Diodes Using a Neutral π Radical as Emitter: The Emission from a Doublet

Peng, Qiming; Obolda, Ablikim; Zhang, Ming; Li, Feng

doi:10.1002/ange.201500242

Cited by 75 publications

(21 citation statements)

References 42 publications

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“…Molecular radicals hold one or more unpaired electrons in their valence orbitals. These molecules have attracted great interest for applications in organic optoelectronic , and spintronic , devices. Unfortunately, the open-shell nature renders these molecules highly reactive.…”

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confidence: 99%

π-Radical Formation by Pyrrolic H Abstraction of Phthalocyanine Molecules on Molybdenum Disulfide

et al. 2019

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For a molecular radical to be stable, the environment needs to be inert. Furthermore, an unpaired electron is less likely to react chemically, when it is placed in an extended orbital. Here, we use the tip of a scanning tunneling microscope to abstract one of the pyrrolic hydrogen atoms from phthalocyanine (H2Pc) deposited on a single layer of molybdenum disulfide (MoS2) on Au(111). We show the successful dissociation reaction by current-induced three-level fluctuations reflecting the inequivalent positions of the remaining H atom in the pyrrole center. Tunneling spectroscopy reveals two narrow resonances inside the semiconducting energy gap of MoS2 with their spatial extent resembling the highest occupied molecular orbital (HOMO) of H2Pc. By comparison to simple density functional calculations of the isolated molecule, we show that these correspond to a single occupation of the Coulomb-split highest molecular orbital of HPc. We conclude that the dangling σ bond after N-H bond cleavage is filled by an electron from the delocalized HOMO. The extended nature of the HOMO together with the inert nature of the MoS2 layer favor the stabilization of this radical state.Molecular radicals hold one or more unpaired electrons in their valence orbitals. These molecules have attracted great interest for applications in organic optoelectronic [1, 2] and spintronic [3, 4] devices. Unfortunately, the open-shell nature renders these molecules highly reactive. Hence, the class of stable molecular radicals is limited. Most promising candidates for stable radicals are molecules with the unpaired electron being hosted in an extended orbital [3, 5]. Such molecules can be obtained, e.g., by dehydrogenation or dehalogenation, where the dissociation reaction involves the highest occupied molecular orbital (HOMO) [6][7][8][9][10][11]. Prime examples for H abstraction are porphyrin and phthalocyanine molecules, where one of the pyrrolic H atoms can be detached by a voltage pulse from the tip of a scanning tunneling microscope (STM) [12,13]. However, when the molecules are placed on a metal substrate the expected radical state is not preserved. Intramolecular relaxations and charge transfer with the substrate lead to a closed-shell configuration [8,14,15]. To suppress the interaction of radical molecules with the substrate, thin insulating layers of NaCl have been employed successfully for several radical species [7][8][9][10][11], but a radical state of H-abstracted Pc has not been reported to date.Here, we show that a monolayer of MoS 2 on Au(111) is an ideal system to study the H-abstraction reaction by STM. We prove the successful dehydrogenation reaction by three-level fluctuations of the tunneling current, reflecting the switching of the position of the single H atom in the pyrrolic center [12]. By mapping the spatial distribution of the singly occupied molecular orbital (SOMO) and singly unoccupied molecular orbital (SUMO), we find that the cleavage of an N-H bond does not lead to a localized dangling bond, but to an extended π rad...

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confidence: 99%

π-Radical Formation by Pyrrolic H Abstraction of Phthalocyanine Molecules on Molybdenum Disulfide

et al. 2019

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“…[57] Li et al reported organic shell-molecule to avoid the transition problem of triplet in OLEDs. [58] They fabricated OLEDs using stable neutral 𝜋 radicals and achieved an EQE of 2.4%. [58] They reported a new stable room-temperature luminescent radical, (N-carbazolyl)bis(2,4,6-tirchlorophenyl)-methyl radical (CzBTM), which exhibited deep red to near infrared emission.…”

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confidence: 99%

Approaches for Long Lifetime Organic Light Emitting Diodes

et al. 2020

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Organic light emitting diodes (OLEDs) have been well known for their potential usage in the lighting and display industry. The device efficiency and lifetime have improved considerably in the last three decades. However, for commercial applications, operational lifetime still lies as one of the looming challenges. In this review paper, an in-depth description of the various factors which affect OLED lifetime, and the related solutions is attempted to be consolidated. Notably, all the known intrinsic and extrinsic degradation phenomena and failure mechanisms, which include the presence of dark spot, high heat during device operation, substrate fracture, downgrading luminance, moisture attack, oxidation, corrosion, electron induced migrations, photochemical degradation, electrochemical degradation, electric breakdown, thermomechanical failures, thermal breakdown/degradation, and presence of impurities within the materials and evaporator chamber are reviewed. Light is also shed on the materials and device structures which are developed in order to obtain along with developed materials and device structures to obtain stable devices. It is believed that the theme of this report, summarizing the knowledge of mechanisms allied with OLED degradation, would be contributory in developing better-quality OLED materials and, accordingly, longer lifespan devices.

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“…To achieve efficient organic NIR emitters, thermally activated delayed fluorescence (TADF) organics (Kim et al, 2018a) and organometallic phosphors based on Pt(II) (Ly et al, 2017), Os(II) (Liao et al, 2015), and Ir(III) complexes (Kim et al, 2018b) which can harness the energy of both 25% singlet and 75% triplet excited states are the most studied materials for getting high EQEs. Meanwhile, the luminescent radicals whose emissions originate from a spin doublet (Peng et al, 2015) are also considered to be one candidate material because the neutral radicals are capable of circumventing the efficiency limitations imposed by the triplet excitons. Under a designed structure of radical-based OLEDs, the selective injections of holes into the highest occupied molecular orbital (HOMO) and electron into the highest singly occupied molecular orbital (SOMO) could be achieved to form the emissive doublet excited state with near 100% internal quantum efficiency (IQE).…”

Section: Introductionmentioning

confidence: 99%

Iridium(III) complexes with 1-phenylisoquinoline-4-carbonitrile units for efficient NIR organic light-emitting diodes

Zhang

Chen

et al. 2021

iScience

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Summary Achieving the high external quantum efficiency (EQE) of near-infrared (NIR) emission in iridium(III) complexes still remains a challenge owing to their unsteady excited states which easily decay to the ground states through the nonradiative pathways. Herein, three Ir(III) phosphors in which the cyclometalated ligand 1-phenylisoquinoline-4-carbonitrile (piq-CN) is functionalized with the cyano, tert- butyl, and dimethyl groups are developed (CN-CNIr, Bu-CNIr, and DM-CNIr, respectively). Three simple synthetic steps can afford this class of deep red to NIR Ir(III) emitters. The organic light-emitting diodes (OLEDs) based on Bu-CNIr and DM-CNIr attain the maximum EQEs of 7.1% and 7.2% with the emission peaks at 695 and 714 nm, respectively. This strategy using substituted piq-CN derivatives as the cyclometalated ligands can offer an effective approach to promote the radiative rate of NIR-emitting Ir(III) materials. An insight into how the electron-withdrawing and electron-donating substituents on ligands influence the optoelectronic properties of their Ir(III) complexes is also provided.

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Organic Light‐Emitting Diodes Using a Neutral π Radical as Emitter: The Emission from a Doublet

Cited by 75 publications

References 42 publications

π-Radical Formation by Pyrrolic H Abstraction of Phthalocyanine Molecules on Molybdenum Disulfide

π-Radical Formation by Pyrrolic H Abstraction of Phthalocyanine Molecules on Molybdenum Disulfide

Approaches for Long Lifetime Organic Light Emitting Diodes

Iridium(III) complexes with 1-phenylisoquinoline-4-carbonitrile units for efficient NIR organic light-emitting diodes

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