Ultra‐Long Lived Luminescent Triplet Excited States in Cyclic (Alkyl)(amino)carbene Complexes of Zn(II) Halides

Mrózek, Ondřej; Gernert, Markus; Belyaev, Andrey; Mitra, Mousree; Janiak, Lars; Marian, Christel M.; Steffen, Andreas

doi:10.1002/chem.202201114

Cited by 21 publications

(31 citation statements)

References 73 publications

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“…One of the most recent fundamental developments concerning photoactive Zn II compounds pursues the idea to introduce other emission types than ligand-based fluorescence, for example, states with triplet and/or charge-transfer character in halide complexes. − To date, this specific research thrust seems to concentrate largely on the solid state, presumably because phosphorescence and charge-transfer emission are trickier to obtain in fluid solution at room temperature. The solution phase is however very relevant for photoactive triplet and charge-transfer excited states, due to possible applications in triplet energy-transfer catalysis, triplet–triplet annihilation upconversion, photoinduced electron transfer, and photoredox catalysis, including perspectives for solar energy conversion .…”

Section: Introductionmentioning

confidence: 99%

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

Kübler

Pfund

Wenger

2022

JACS Au

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

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Section: Introductionmentioning

confidence: 99%

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

Kübler

Pfund

Wenger

2022

JACS Au

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“…In light of current developments in photoactive d 10 metal complexes, − we were therefore interested in studying the effect of different diborene and metal substituents as well as the nature of the metal center on the photostability and emissive properties of diborene coinage metal π complexes, in the hope of enhancing ISC and making phosphorescence from the T 1 state accessible.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Fluorescence Studies of Diborene Coinage Metal Complexes

et al. 2022

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Nine different coinage metal (Cu, Ag) π complexes of diborenes with various anionic diborene (aryl, heteroaryl) and metal substituents (Cl, Br, C 6 F 5 , C 2 SiMe 3 ), stabilizing neutral donors (N-heterocyclic carbene = NHC, phosphine), configurations (cis/trans, acyclic/cyclic diborene), and charges (neutral, cationic) were synthesized and characterized by multinuclear NMR spectroscopy and X-ray crystallographic analyses. Their optical properties were investigated by UV−vis absorption and steadystate as well as time-resolved luminescence spectroscopy in solution and the solid state to gain insights into the excited-state behavior of this unusual class of photoactive compounds and to provide structure−property relationships. The structural and electronic modification of the (B�B)•••M motif greatly influences not only the visible light absorption but also the photostability and quantum yields, which can reach high values of up to f = 0.42. The lifetimes are found in the nanosecond regime, providing estimated radiative rate constants over a wide range of k r = 1.3−14 × 10 7 s −1 , indicative of fluorescence. Intersystem crossing (ISC) is sufficiently slow for prompt emission from the S 1 state to be observed, while the spin−orbit coupling in the T 1 state is too weak for phosphorescence to occur at room temperature. ISC can be accelerated, however, by modifying diborene ligand substitution and the coinage metal center, hinting at the potential for exploiting the properties of long-lived triplet excited states of metal diborene complexes in the future.

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“…Therefore, the propensity of MLCT states is low in Zn(II). Formerly investigated zinc complexes mainly showed prompt fluorescence and only a few were reported to be phosphorescent. − A recent re-investigation of the photophysical behavior of zinc(II) diimine bis-thiolate complexes revealed that their room-temperature LLCT emission actually shows TADF characteristics . With regard to lighting applications, Zn(II) complexes were mostly employed as fluorescent emitters or hosts for fluorescent and phosphorescent dopants. − The growing interest in new TADF-based OLED emitters strongly promoted research on Zn(II) emitters.…”

Section: Introductionmentioning

confidence: 99%

Finding Design Principles of OLED Emitters through Theoretical Investigations of Zn(II) Carbene Complexes

2022

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In this work, Zn(II) carbene complexes carrying a dianionic 1,2-dithiolbenzene (dtb) or 1,2-diolbenzene (dob) ligand were investigated regarding their suitability as organic light-emitting diode (OLED) emitter. For the optimization of the complexes, density functional-based methods were used and frequency analyses verified the obtained structures as minima. All calculations were carried out including a polarizable continuum model to mimic solvent−solute interactions. Multireference configuration interaction methods were used to determine excitation energies, spin-orbit couplings, and luminescence properties. Rate constants of spinallowed and spin-forbidden transitions were calculated according to a Fermi golden rule expression. Using carbene ligands with varying σ-donor and π-acceptor strengths, the luminescence is found to be tunable from yellow to orange/red to deep red/nearinfrared. The calculated intersystem crossing (ISC) time constants indicate thermally activated delayed fluorescence (TADF) to be the main decay channel. In contrast to many d 10 coinage metal complexes, a parallel orientation of dtb or dob and the carbene ligand is found to be highly favorable. For the complexes with a cyclic (alkyl)(amino) carbene (CAAC) or cyclic (amino)(aryl) carbene (CAArC) ligand, the S 1 and T 1 states have ligand-to-ligand charge-transfer (LLCT) character and are energetically close. The complex with a classical N-heterocyclic carbene (NHC) ligand has S 1 and T 1 states with mixed ligand-to-metal charge-transfer (LMCT)/LLCT character and is a very rare example in which the zinc ion contributes to the excitation.

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Ultra‐Long Lived Luminescent Triplet Excited States in Cyclic (Alkyl)(amino)carbene Complexes of Zn(II) Halides

Cited by 21 publications

References 73 publications

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

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

Synthesis and Fluorescence Studies of Diborene Coinage Metal Complexes

Finding Design Principles of OLED Emitters through Theoretical Investigations of Zn(II) Carbene Complexes

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