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, Год журнала: 2023, Номер 145(9), С. 4903 - 4920

Опубликована: Фев. 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.

Язык: Английский

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Leveraging Intramolecular π-Stacking to Access an Exceptionally Long-Lived ³MC Excited State in an Fe(II) Carbene Complex

Journal of the American Chemical Society, Год журнала: 2025, Номер 147(2), С. 1694 - 1708

Опубликована: Янв. 6, 2025

The ability to manipulate excited-state decay cascades using molecular structure is essential the application of abundant-metal photosensitizers and chromophores. Ligand design has yielded some spectacular results elongating charge-transfer excited state lifetimes Fe(II) coordination complexes, but triplet metal-centered (3MC) states─recently demonstrated be critical photoactivity isoelectronic Co(III) polypyridyls─have date remained elusive, with temporally isolable examples limited picosecond regime. With this report, we show how strong-field donors intramolecular π-stacking can conspire stabilize a long-lived 3MC for remarkable 4.1 ± 0.3 ns in fluid solution at ambient temperature. Analysis variable-temperature time-resolved absorption data theoretical models ranging from Arrhenius semiclassical Marcus theory, combined computational modeling X-ray crystallography, reveal Jahn-Teller stabilized high activation barrier ground-state recovery. net result chromophore lifetime that orders magnitude longer than anything yet observed an complex.

Язык: Английский

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Charge‐Transfer and Spin‐Flip States: Thriving as Complements

Angewandte Chemie International Edition, Год журнала: 2022, Номер 62(15)

Опубликована: Окт. 4, 2022

Abstract Transition metal complexes with photoactive charge‐transfer excited states are pervasive throughout the literature. In particular, [Ru(bpy) 3 ] 2+ (bpy=2,2′‐bipyridine), its metal‐to‐ligand emission, has been established as a key complex. Meanwhile, interest in so‐called spin‐flip metal‐centered risen dramatically after molecular ruby [Cr(ddpd) 2 3+ (ddpd= N , ′‐dimethyl‐ ′‐dipyridin‐2‐yl‐pyridine‐2,6‐diamine) led to design principles access strong, long‐lived emission from photostable chromium(III) complexes. This Review contrasts properties of emissive and by using prototypical examples. We discuss relevant states, tunability their energy lifetimes, response external stimuli. Finally, we identify strengths weaknesses applications such photocatalysis circularly polarized luminescence.

Язык: Английский

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Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

JACS Au, Год журнала: 2022, Номер 2(10), С. 2367 - 2380

Опубликована: Окт. 11, 2022

Many CuI complexes have luminescent triplet charge-transfer excited states with diverse applications in photophysics and photochemistry, but for isoelectronic ZnII compounds, this behavior is much less common, they typically only show ligand-based fluorescence from singlet π–π* states. We report two closely related tetrahedral which intersystem crossing occurs appreciable quantum yields leads to the population of intraligand (ILCT) character. In addition showing their initially 1ILCT states, these new compounds therefore undergo triplet–triplet energy transfer (TTET) 3ILCT consequently can act as sensitizers photo-isomerization reactions annihilation upconversion blue ultraviolet spectral range. The photoactive state furthermore facilitates photoinduced electron transfer. Collectively, our findings demonstrate that mononuclear photophysical photochemical properties reminiscent well-known are accessible suitable ligands potentially amenable many different applications. Our insights seem relevant greater context obtaining based on abundant transition metals, complementing precious-metal-based luminophores photosensitizers.

Язык: Английский

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Molecular Design Principles to Elongate the Metal-to-Ligand Charge Transfer Excited-State Lifetimes of Square-Planar Nickel(II) Complexes

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(48), С. 21948 - 21960

Опубликована: Ноя. 23, 2022

Square-planar NiII complexes and their electronically excited states play key roles in cross-coupling catalysis could offer new opportunities to complement well-known isoelectronic PtII luminophores. Metal-to-ligand charge transfer (MLCT) deactivation pathways are particularly relevant these contexts. We sought extend the lifetimes of 3MLCT square-planar by creating coordination environments that seemed well adapted 3d8 valence electron configuration. Using a rigid tridentate chelate ligand, which central cyclometalated phenyl unit is flanked two coordinating N-heterocyclic carbenes, along with monodentate isocyanide very strong ligand field created. Bulky substituents at backbone furthermore protect center from nucleophilic attack axial directions. UV-Vis transient absorption spectroscopies reveal upon excitation into 1MLCT bands ultrafast intersystem crossing state, latter relaxes onward metal-centered triplet state (3MC). A torsional motion NiII-carbon bond elongation facilitate relaxation 3MC state. The lifetime gets longer increasing strength improved steric protection, thereby revealing clear design guidelines for enhanced photophysical properties. longest reached solution room temperature 48 ps, factor 5-10 compared previously investigated complexes. Our study contributes making first-row transition metal partially filled d-orbitals more amenable applications photophysics photochemistry.

Язык: Английский

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

Angewandte Chemie International Edition, Год журнала: 2023, Номер 62(30)

Опубликована: Апрель 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.

Язык: Английский

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Factors that Impact Photochemical Cage Escape Yields

Chemical Reviews, Год журнала: 2024, Номер 124(11), С. 7379 - 7464

Опубликована: Май 14, 2024

The utilization of visible light to mediate chemical reactions in fluid solutions has applications that range from solar fuel production medicine and organic synthesis. These are typically initiated by electron transfer between a photoexcited dye molecule (a photosensitizer) redox-active quencher yield radical pairs intimately associated within solvent cage. Many these radicals undergo rapid thermodynamically favored "geminate" recombination do not diffuse out the cage surrounds them. Those escape useful reagents may subsequent important above-mentioned applications. process factors determine yields remain poorly understood despite decades research motivated their practical fundamental importance. Herein, state-of-the-art on light-induced appeared since seminal 1972 review J. P. Lorand entitled "The Cage Effect" is reviewed. This also provides some background for those new field discusses both homolytic bond photodissociation bimolecular induced reactions. concludes with key goals directions future promise elevate this very vibrant even greater heights.

Язык: Английский

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

Journal of the American Chemical Society, Год журнала: 2024, Номер unknown

Опубликована: Апрель 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.

Язык: Английский

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Rationalizing Photophysics of Co(III) Complexes with Pendant Pyrene Moieties

Inorganic Chemistry, Год журнала: 2025, Номер unknown

Опубликована: Янв. 9, 2025

Pendant organic chromophores have been used to improve the photocatalytic performance of many metal-based photosensitizers, particularly in first-row metals, by increasing π conjugation ligands and lowering energy photoactive absorption band. Using a combination spectroscopic studies computational modeling, we rationalize excited state dynamics Co(III) complex containing pendant pyrene moieties, CoL1, where L1 = 1,1′-(4-(pyren-1-yl)pyridine-2,6-diyl)bis(3-methyl-1H-imidazol-3-ium). CoL1 displays higher visible absorptivity, blue luminescence from singlet states compared with CoL0 [L0 1,1′-(pyridine-2,6-diyl)bis(3-methyl-1H-imidazol-3-ium)] which moiety is absent. Emissive properties are highly influenced metal center, reducing fluorescence lifetime 5.9 3.5 ns, shift 43 nm. The lower d orbitals Fe(II) drastically affects character state, resulting mixture intraligand charge-transfer (1ILCT) ligand-to-metal (1LMCT) character. Transient experiments revealed that although dark triplet (3ILPyrene) present, it not efficiently populated possesses short nanosecond-scale lifetime. Instead, metal-centered (3MC) dominate decay path 2.4 ps lifetime, no photoactivity toward oxygen formation or triplet–triplet transfer (TTET). This work shows how various factors can influence excited-state dynamics.

Язык: Английский

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Low Temperature Emissive Cyclometalated Cobalt(III) Complexes

Inorganic Chemistry, Год журнала: 2025, Номер unknown

Опубликована: Янв. 14, 2025

A series of CoIII complexes [Co(RImP)2][PF6], with HMeImP = 1,1'-(1,3-phenylene)bis(3-methyl-1-imidazole-2-ylidene)) and R Me, Et, iPr, nBu, is presented in this work. The influence the strong donor ligand on ground excited-state photophysical properties was investigated context different alkyl substituents at imidazole nitrogen. X-ray diffraction revealed no significant alterations structures all differences emerge from electronic structures. These were probed via cyclic voltammetry UV-vis spectroscopy, detailing ground-state properties. All are emissive 77 K a 3MC state, which exhibits lifetimes range 1-5 ns room temperature, depending substituent. Therefore, it clearly shown that even small structure have large impact details excited state landscape. observed behavior rationalized by detailed DFT analysis, shows minimum-energy crossing point to located only slightly above MC energy: Consequently, nonradiative decay temperature enabled, while path prohibited, leading low-temperature emission.

Язык: Английский

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