Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d⁶ Complexes with Cr⁰, Mn^I, Fe^II, and Co^III

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(9), P. 4903 - 4920

Published: Feb. 21, 2023

Many coordination complexes and organometallic compounds with the 4d6 5d6 valence electron configurations have outstanding photophysical photochemical properties, which stem from metal-to-ligand charge transfer (MLCT) excited states. This substance class makes extensive use of most precious least abundant metal elements, consequently there has been a long-standing interest in first-row transition photoactive MLCT Semiprecious copper(I) its completely filled 3d subshell is relatively straightforward well explored case, but 3d6 partially d-orbitals lead to energetically low-lying metal-centered (MC) states that can cause undesirably fast state deactivation. Herein, we discuss recent advances made isoelectronic Cr0, MnI, FeII, CoIII compounds, for long-lived become accessible over past five years. Furthermore, possible future developments search new subshells next-generation applications photophysics photochemistry.

Language: Английский

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Mechanisms of Photoredox Catalysis Featuring Nickel–Bipyridine Complexes

ACS Catalysis, Journal Year: 2024, Volume and Issue: 14(11), P. 9055 - 9076

Published: May 29, 2024

Metallaphotoredox catalysis can unlock useful pathways for transforming organic reactants into desirable products, largely due to the conversion of photon energy chemical potential drive redox and bond transformation processes. Despite importance these processes cross-coupling reactions other transformations, their mechanistic details are only superficially understood. In this review, we have provided a detailed summary various photoredox mechanisms that been proposed date Ni-bipyridine (bpy) complexes, focusing separately on photosensitized direct excitation reaction By highlighting multiple key findings, depict how mechanisms, which ultimately define substrate scope, themselves defined by ground- excited-state geometric electronic structures Ni-based intermediates. We further identify knowledge gaps motivate future studies development synergistic research approaches spanning physical, organic, inorganic chemistry communities.

Language: Английский

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Excited Organic Radicals in Photoredox Catalysis

JACS Au, Journal Year: 2025, Volume and Issue: 5(2), P. 426 - 447

Published: Jan. 29, 2025

Many important synthetic-oriented works have proposed excited organic radicals as photoactive species, yet mechanistic studies raised doubts about whether they can truly function photocatalysts. This skepticism originates from the formation of (photo)redox-active degradation products and picosecond decay electronically radicals, which is considered too short for diffusion-based photoinduced electron transfer reactions. From this perspective, we analyze synthetic transformations where been photocatalysts, comparing their theoretical maximum state potentials with required observed photocatalytic reactivity. We summarize structurally similar photocatalysts indicating different reaction pathways some catalytic systems, addressing cases radical exceed Additionally, perform a kinetic analysis to explain in on subpicosecond time scales. further rationalize potential anti-Kasha reactivity higher states femtosecond lifetimes, highlighting how future photocatalysis advancements could unlock new photochemical pathways.

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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The Nephelauxetic Effect Becomes an Important Design Factor for Photoactive First‐Row Transition Metal Complexes

Angewandte Chemie International Edition, Journal Year: 2023, Volume and Issue: 62(30)

Published: April 14, 2023

Abstract The expansion of d‐orbitals as a result metal‐ligand bond covalence, the so‐called nephelauxetic effect, is well‐established concept coordination chemistry, yet its importance for design new photoactive complexes based on first‐row transition metals only beginning to be recognized. Until recently, much focus has been optimizing ligand field strength, geometries, and molecular rigidity, but now it becomes evident that effect can game changer regarding photophysical properties 3d metal in solution at room temperature. In Cr III Mn IV with d 3 valence electron configuration, was exploited shift well‐known ruby‐like red luminescence near‐infrared spectral region. Fe II Co low‐spin 6 charge‐transfer excited states were stabilized respect detrimental metal‐centered states, improve their enhance application potential. isoelectronic (3d ) isocyanide 0 I , likely play well, enabling other favorable photoreactivity. This minireview illustrates broad applicability tailoring photochemical compounds made from abundant metals.

Language: Английский

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Improved transition metal photosensitizers to drive advances in photocatalysis

Chemical Science, Journal Year: 2023, Volume and Issue: 15(1), P. 77 - 94

Published: Nov. 24, 2023

To function effectively in a photocatalytic application, photosensitizer's light absorption, excited-state lifetime, and redox potentials, both the ground state excited state, are critically important. The absorption profile is particularly relevant to applications involving solar harvesting, whereas potentials lifetimes determine thermodynamics, kinetics, quantum yields of photoinduced processes. This perspective article focuses on synthetic inorganic organometallic approaches optimize these three characteristics transition-metal based photosensitizers. We include our own work areas, which has focused extensively exceptionally strong cyclometalated iridium photoreductants that enable challenging reductive photoredox transformations organic substrates, more recent led improved harvesting charge-transfer copper(i) chromophores, an emerging class earth-abundant compounds solar-energy applications. also highlight many other complementary strategies for optimizing parameters representative examples from literature. It remains significant challenge simultaneously all at once, since improvements one often come detriment others. These inherent trade-offs obviate or circumvent them discussed throughout.

Language: Английский

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Halide Noninnocence and Direct Photoreduction of Ni(II) Enables Coupling of Aryl Chlorides in Dual Catalytic, Carbon–Heteroatom Bond-Forming Reactions

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(22), P. 12293 - 12304

Published: May 19, 2023

Recent mechanistic studies of dual photoredox/Ni-catalyzed, light-driven cross-coupling reactions have found that the photocatalyst (PC) operates through either reductive quenching or energy transfer cycles. To date, reports invoking oxidative cycles are comparatively rare and direct observation such a event has not been reported. However, when PCs with highly reducing excited states used (e.g., Ir(ppy)

Language: Английский

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Nickel(II) Analogues of Phosphorescent Platinum(II) Complexes with Picosecond Excited‐State Decay

Angewandte Chemie International Edition, Journal Year: 2023, Volume and Issue: 62(46)

Published: Sept. 21, 2023

Square-planar NiII complexes are interesting as cheaper and more sustainable alternatives to PtII luminophores widely used in lighting photocatalysis. We investigated the excited-state behavior of two complexes, which isostructural with luminescent complexes. The initially excited singlet metal-to-ligand charge transfer (1 MLCT) states decay metal-centered (3 MC) within less than 1 picosecond, followed by non-radiative relaxation 3 MC electronic ground state 9-21 ps. This contrasts population an emissive triplet ligand-centered LC) upon excitation analogues. Structural distortions responsible for this discrepant lead dark far lower energy LC compounds. Our findings suggest that if these structural could be restricted rigid coordination environments stronger ligand fields, four-coordinate decelerated such or MLCT become accessible. These insights relevant make fit photophysical photochemical applications relied on until now.

Language: Английский

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Advances in sprayable sensors for nerve agent detection

Coordination Chemistry Reviews, Journal Year: 2024, Volume and Issue: 509, P. 215804 - 215804

Published: March 22, 2024

Language: Английский

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Controlling the Photophysical Properties of a Series of Isostructural d⁶ Complexes Based on Cr⁰, Mn^I, and Fe^II

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(7), P. 4605 - 4619

Published: Feb. 9, 2024

Development of first-row transition metal complexes with similar luminescence and photoredox properties as widely used RuII polypyridines is attractive because metals from the first series are comparatively abundant inexpensive. The weaker ligand field experienced by valence d-electrons challenges installation same types metal-to-ligand charge transfer (MLCT) excited states in precious complexes, due to rapid population energetically lower-lying metal-centered (MC) states. In a family isostructural tris(diisocyanide) 3d6 Cr0, MnI, FeII, increasing effective nuclear strength allow us control energetic order between 3MLCT 3MC states, whereas pyrene decoration isocyanide framework provides over intraligand (ILPyr) chromium(0) complex shows red phosphorescence all other higher energy. manganese(I) complex, microsecond-lived dark 3ILPyr state, reminiscent electronic encountered many polyaromatic hydrocarbon compounds, lowest becomes photoactive. iron(II) MLCT state has shifted so much energy that 1ILPyr fluorescence occurs, parallel excited-state deactivation pathways. Our combined synthetic-spectroscopic-theoretical study unprecedented insights into how charge, strength, π-conjugation affect ligand-based under what circumstances these individual become luminescent exploitable photochemistry. Such key further developments photoredox-active complexes.

Language: Английский

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