Two-Coordinate Thermally Activated Delayed Fluorescence Coinage Metal Complexes: Molecular Design, Photophysical Characters, and Device Application

Chemical Reviews, Journal Year: 2024, Volume and Issue: 124(7), P. 4332 - 4392

Published: March 28, 2024

Since the emergence of first green light emission from a fluorescent thin-film organic emitting diode (OLED) in mid-1980s, global consumer market for OLED displays has flourished over past few decades. This growth can primarily be attributed to development noble metal phosphorescent emitters that facilitated remarkable gains electrical conversion efficiency, broadened color gamut, and vibrant image quality displays. Despite these achievements, limited abundance metals Earth's crust spurred ongoing efforts discover cost-effective electroluminescent materials. One particularly promising avenue is exploration thermally activated delayed fluorescence (TADF), mechanism with potential fully harness excitons OLEDs. Recently, investigations have unveiled TADF series two-coordinate coinage (Cu, Ag, Au) complexes. These organometallic materials exhibit distinctive behavior comparison their counterparts. They offer benefits such as tunable emissive colors, short lifetimes, high luminescent quantum yields, reasonable stability. Impressively, both vacuum-deposited solution-processed OLEDs incorporating achieved outstanding performance. review encompasses various facets on complexes, including molecular design, photophysical characterizations, elucidation structure–property relationships, applications.

Language: Английский

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Luminescent N^C^N Pincer Ni(II), Pd(II), and Pt(II) Complexes with a Pendant Coumarin Group: The Role of Auxiliary Ligands and Environments

Inorganic Chemistry, Journal Year: 2025, Volume and Issue: unknown

Published: Feb. 26, 2025

Square-planar d8-configured metal complexes and their excited states play a key role in photocatalysis, sensing, optoelectronic devices. However, metal-to-ligand charge-transfer (MLCT) involving transition metals, particularly those with 3d8 electronic configuration, present challenges due to rapid nonradiative relaxation via low-lying metal-centered (MC) states. In this work, an isoelectronic isostructural series of cyclometalated [MX(dpb)] M = Ni(II), Pd(II), Pt(II), dpb 1,3-di(2-pyridyl)phenide, auxiliary ligand X chlorido, azido, triazolato were studied by UV/vis absorption, steady-state, time-resolved photoluminescence spectroscopy solution frozen glassy matrix at 77 K, along DFT calculations. Consistently, the Pd(II) Pt(II) exhibited characteristic emission from triplet ligand-centered (3LC) contrast, Ni(II) triazolatoCOOCH3,COOCH3 ligands nonemissive low room temperatures, presence MC-type ligand-field On other hand, [Ni(triazolatoCoumarin,COOCH3)(dpb)] showed phosphorescence T5 state since restrictive environment limits structural relaxation, while temperature, primary is singlet LC coumarin moiety free ligand.

Language: Английский

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Iron(III) Carbene Complexes with Tunable Excited State Energies for Photoredox and Upconversion

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: unknown

Published: April 10, 2024

Substituting precious elements in luminophores and photocatalysts by abundant first-row transition metals remains a significant challenge, iron continues to be particularly attractive owing its high natural abundance low cost. Most complexes known date face severe limitations due undesirably efficient deactivation of luminescent photoredox-active excited states. Two new iron(III) with structurally simple chelate ligands enable straightforward tuning ground state properties, contrasting recent examples, which chemical modification had minor impact. Crude samples feature two luminescence bands strongly reminiscent complex, this observation was attributed dual luminescence, but our case, there is clear-cut evidence that the higher-energy stems from an impurity only red photoluminescence doublet ligand-to-metal charge transfer (2LMCT) genuine. Photoinduced oxidative reductive electron reactions methyl viologen 10-methylphenothiazine occur nearly diffusion-limited kinetics. Photocatalytic not previously reported for compound class, particular C–H arylation diazonium salts aerobic hydroxylation boronic acids, were achieved low-energy light excitation. Doublet–triplet energy (DTET) 2LMCT anthracene annihilator permits proof principle triplet–triplet annihilation upconversion based on molecular photosensitizer. These findings are relevant development featuring photophysical photochemical properties competitive noble-metal-based compounds.

Language: Английский

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Ultrafast Photophysics of Ni(I)–Bipyridine Halide Complexes: Spanning the Marcus Normal and Inverted Regimes

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(22), P. 15506 - 15514

Published: May 22, 2024

Owing to their light-harvesting properties, nickel–bipyridine (bpy) complexes have found wide use in metallaphotoredox cross-coupling reactions. Key these transformations are Ni(I)–bpy halide intermediates that absorb a significant fraction of light at relevant reaction irradiation wavelengths. Herein, we report ultrafast transient absorption (TA) spectroscopy on library eight complexes, the first such characterization any Ni(I) species. The TA data reveal formation and decay Ni(I)-to-bpy metal-to-ligand charge transfer (MLCT) excited states (10–30 ps) whose relaxation dynamics well described by vibronic Marcus theory, spanning normal inverted regions as result simple changes bpy substituents. While lifetimes relatively long for MLCT first-row transition metal duration precludes excited-state bimolecular reactivity photoredox We also present one-step method generate an isolable, solid-state species, which decouples light-initiated from dark, thermal cycles catalysis.

Language: Английский

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Light Activation and Photophysics of a Structurally Constrained Nickel(II)–Bipyridine Aryl Halide Complex

Inorganic Chemistry, Journal Year: 2024, Volume and Issue: 63(9), P. 4120 - 4131

Published: Feb. 20, 2024

Transition-metal photoredox catalysis has transformed organic synthesis by harnessing light to construct complex molecules. Nickel(II)–bipyridine (bpy) aryl halide complexes are a significant class of cross-coupling catalysts that can be activated via direct excitation. This study investigates the effects molecular structure on photophysics these considering an underexplored, structurally constrained Ni(II)–bpy in which and bpy ligands covalently tethered alongside traditional unconstrained complexes. Intriguingly, is photochemically stable but features reversible Ni(II)–C(aryl) ⇄ [Ni(I)···C(aryl)•] equilibrium upon photoexcitation. When electrophile introduced during photoirradiation, we demonstrate preference for photodissociation over recombination, rendering parent Ni(II) source reactive Ni(I) intermediate. Here, characterize photochemical behavior kinetic analyses, quantum chemical calculations, ultrafast transient absorption spectroscopy. Comparison previously characterized indicates structural constraints considered here dramatically influence excited state relaxation pathway provide insight into characteristics excited-state Ni(II)–C bond homolysis radical reassociation dynamics. enriches understanding offers new possibilities designing customized photoactive precise synthesis.

Language: Английский

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Structural Control of Highly Efficient Thermally Activated Delayed Fluorescence in Carbene Zinc(II) Dithiolates**

Angewandte Chemie International Edition, Journal Year: 2023, Volume and Issue: 63(7)

Published: Dec. 8, 2023

Abstract Luminescent metal complexes based on earth abundant elements are a valuable target to substitute 4d/5d transition as triplet emitters in advanced photonic applications. Whereas Cu I have been thoroughly investigated the last two decades for this purpose, no structure‐property‐relationships efficient luminescence involving excited states from Zn II established. Herein, we report design of monomeric carbene zinc(II) dithiolates (CZT) featuring donor‐acceptor‐motif that leads highly thermally activated delayed fluorescence (TADF) with compounds unprecedented radiative rate constants k TADF =1.2×10 6 s −1 at 297 K. Our high‐level DFT/MRCI calculations revealed relative orientation ligands involved ligand‐to‐ligand charge transfer ( 1/3 LLCT) is paramount control process. Specifically, dihedral angle 36–40° very reverse intersystem‐crossing (rISC) order 10 9 due spin‐orbit coupling (SOC) mediated by sulfur atoms combination small ΔE S1‐T1 ca. 56 meV.

Language: Английский

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Luminescent and Photoredox‐Active Molybdenum(0) Complexes Competitive with Isoelectronic Ruthenium(II) Polypyridines

Angewandte Chemie International Edition, Journal Year: 2023, Volume and Issue: 63(10)

Published: Oct. 27, 2023

Ruthenium(II) complexes with chelating polypyridine ligands are among the most frequently investigated compounds in photophysics and photochemistry, owing to their favorable luminescence photoredox properties. Equally good photoluminescence performance attractive photocatalytic behavior is now achievable isoelectronic molybdenum(0) complexes. The zero-valent oxidation state of molybdenum stabilized by carbonyl or isocyanide ligands, metal-to-ligand charge transfer (MLCT) excited states analogous those ruthenium(II) can be established. Microsecond MLCT excited-state lifetimes quantum yields up 0.2 have been achieved solution at room temperature, emission wavelength has become tunable over a large range. stronger photoreductants than polypyridines therefore perform more challenging chemical reductions. triplet nature luminescent allows sensitization photon upconversion via triplet-triplet annihilation, convert low-energy input radiation into higher-energy output fluorescence. This review summarizes current art concerning highlights application potential. Molybdenum roughly 140 times abundant far cheaper ruthenium, hence this research relevant greater context finding sustainable alternatives using precious rare transition metals photochemistry.

Language: Английский

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Dinuclear Cyclometalated Pincer Nickel(II) Complexes with Metal‐Metal‐to‐Ligand Charge Transfer Excited States and Near‐Infrared Emission

Angewandte Chemie International Edition, Journal Year: 2024, Volume and Issue: 64(2)

Published: Sept. 25, 2024

Abstract Facile non‐radiative decay of low‐lying metal‐centered (MC) dd excited states has been well documented to pose a significant obstacle the development phosphorescent Ni II complexes due substantial structural distortions between state and ground state. Herein, we prepared series dinuclear 2 II,II by using strong σ‐donating carbene‐phenyl‐carbene (C NHC C phenyl ) pincer ligands, their Pt Pd analogues. Dinuclear bridged formamidinate/α‐carbolinato ligand exhibit short Ni−Ni distances 2.947–3.054 Å singlet metal‐metal‐to‐ligand charge transfer ( 1 MMLCT) transitions at 500–550 nm. Their MMLCT absorption energies are red‐shifted relative analogues ~450 nm ≤420 respectively. One‐electron oxidation these produces valence‐trapped II,III species, which characterized EPR spectroscopy. Upon photoexcitation, display phosphorescence (τ=2.6–8.6 μs) in NIR (800–1400 nm) spectral region 2‐MeTHF solid 77 K, is insensitive π‐conjugation coordinated [C ] ligand. Combined with DFT calculations, emission assigned originate from 3 Studies have found that complex can sensitize formation oxygen catalyze cyclo‐dienes under light irradiation.

Language: Английский

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Activating the Fluorescence of a Ni(II) Complex by Energy Transfer

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(13), P. 8858 - 8864

Published: March 21, 2024

Luminescence of open-shell 3d metal complexes is often quenched due to ultrafast intersystem crossing (ISC) and cooling into a dark metal-centered excited state. We demonstrate successful activation fluorescence from individual nickel phthalocyanine (NiPc) molecules in the junction scanning tunneling microscope (STM) by resonant energy transfer other phthalocyanines at low temperature. By combining STM, spectroscopy, STM-induced luminescence, photoluminescence experiments as well time-dependent density functional theory, we provide evidence that there an barrier for ISC, which, most experimental conditions, overcome. show this also case electroluminescent tunnel where NiPc adsorbed on ultrathin NaCl decoupling film Ag(111) substrate are probed. However, when MPc (M = Zn, Pd, Pt) molecule placed close means STM atomic manipulation, can excite without overcoming ISC barrier, leading Q-band fluorescence. This work demonstrates thermally activated population states be avoided designed local environment temperatures paired with directed molecular excitation vibrationally cold electronic states. Thus, envisage use luminophores based more abundant transition do not rely Pt or Ir restricting vibration-induced ISC.

Language: Английский

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Excited State Covalency, Dynamics, and Photochemistry of Square Planar Ni-Thiolate Complexes Revealed by Ultrafast X-ray Absorption

Journal of the American Chemical Society, Journal Year: 2025, Volume and Issue: 147(9), P. 7496 - 7506

Published: Feb. 24, 2025

Highly covalent Ni bis(dithiolene) and related complexes provide an ideal platform for investigating the effects of metal-ligand orbital hybridization on excited state character dynamics. In particular, we focus ligand field states that dominate photophysics first-row transition metal complexes. We investigate if they can be significantly delocalized off center, possibly yielding photochemical reactivity more similar to charge transfer than metal-centered states. Here, [Ni(mpo)2] (mpo = 2-mercaptopyridine-N-oxide) provides a representative example larger chemical class is active electro- photocatalyst proton reduction. A detailed characterization electronic structure, dynamics, photochemistry presented based ultrafast transient X-ray absorption spectroscopy at S 1s core K-edges. By comparing K-edge ab initio calculations, identify relaxation mechanism where initial ligand-to-metal excitation results in both electron (generating catalytically relevant reduced photoproduct [Ni(mpo)2]-) pseudotetrahedral triplet state. From absorption, found highly onto thiolate ligands, tetrahedral structural distortion shown substantially influence degree delocalization. The significant coordinate target when aiming control covalency square planar

Language: Английский

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