Long-Lived, Strongly Emissive, and Highly Reducing Excited States in Mo(0) Complexes with Chelating Isocyanides

Herr, Patrick; Glaser, Felix; Büldt, Laura A.; Larsen, Christopher B.; Wenger, Oliver S.

doi:10.1021/jacs.9b07373

Cited by 81 publications

(165 citation statements)

References 119 publications

(262 reference statements)

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“…The radiative rate constants of the two Mo 0 complexes are roughly a factor of 2 larger than for the Ru II complex. This is in line with more strongly absorbing MLCT features for [Mo(L Me ) 3 ] and [Mo(L tBu ) 3 ] (with ε max up to 27,000 M −1 cm −1 ) compared to [Ru(dmb) 3 ] 2+ (ε max ≈ 16,500 M −1 cm −1 , ε max is the extinction coefficient at the 1 MLCT absorption band maximum) [27]. However, it should be kept in mind that these are 1 MLCT absorption bands whereas the k r values are for 3 MLCT relaxation.…”

Section: Resultssupporting

confidence: 81%

“…Similarly, the 3 MLCT lifetime (τ) is roughly a factor of 10 longer for [Mo(L tBu ) 3 ] compared to [Mo(L Me ) 3 ]. (In a prior study we already noted that the tert-butyl decorated complex exhibits bi-exponential luminescence decays and transient absorption kinetics in all solvents investigated, and this is likely due to conformational equilibria in solution [27]). The parallel combined trends in luminescence quantum yields and lifetimes indicate that the rate for nonradiative 3 MLCT relaxation (k nr ) decreases by circa a factor of 10 between [Mo(L Me ) 3 ] and [Mo(L tBu ) 3 ], whereas the radiative relaxation rate (k r ) remains similar.…”

Section: Resultsmentioning

confidence: 77%

“…The [Mo(L Me ) 3 ] and [Mo(L tBu ) 3 ] complexes differ only by the substituents in orthoand para-position to the isocyanide groups, yet their photoluminescence properties are very disparate (Table 1) [27]. Whilst the emissive excited state is of 3 MLCT-type in both cases, the luminescence quantum yield (ϕ em ) for [Mo(L tBu ) 3 ] (in de-aerated solution at 20 • C) is an order of magnitude higher than for [Mo(L Me ) 3 ] under identical conditions.…”

Section: Resultsmentioning

confidence: 99%

“…τ −1 = k r + k nr (1) 2+ 3,4 0.83 10.6 1 In toluene. 2 Weighted average of lifetime values (τ) used for the calculation (0.85 × 1110 ns + 0.15 × 2330 ns) [27]. 3 In acetonitrile.…”

Section: Resultsmentioning

confidence: 99%

“…Herein, we provide the first analysis of relevant 3 MLCT excited-state distortions in tris(diisocyanide) Mo 0 complexes, and new temperature-dependent luminescence lifetime data give insight into thermally activated nonradiative relaxation via metal-centered excited states. Recently we reported that the [Mo(L tBu ) 3 ] complex exhibits much more favorable photophysical properties than the closely related [Mo(L Me ) 3 ] compound, and we demonstrated that [Mo(L tBu ) 3 ] is more widely applicable in photoredox catalysis due to greater photo-robustness [27]. The present article focuses on the origin of the photophysical differences between these two complexes and attempts to identify possible reasons for the very favorable luminescence behavior of [Mo(L tBu ) 3 ] in comparison to [Ru(bpy) 3 ] 2+ (bpy = 2,2 -bipyridine) and related Ru II polypyridines.…”

Section: Introductionmentioning

confidence: 92%

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Excited-State Relaxation in Luminescent Molybdenum(0) Complexes with Isocyanide Chelate Ligands

Herr

Wenger

2020

Inorganics

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Diisocyanide ligands with a m-terphenyl backbone provide access to Mo 0 complexes exhibiting the same type of metal-to-ligand charge transfer (MLCT) luminescence as the well-known class of isoelectronic Ru II polypyridines. The luminescence quantum yields and lifetimes of the homoleptic tris(diisocyanide) Mo 0 complexes depend strongly on whether methyl-or tert-butyl substituents are placed in α-position to the isocyanide groups. The bulkier tert-butyl substituents lead to a molecular structure in which the three individual diisocyanides ligated to one Mo 0 center are interlocked more strongly into one another than the ligands with the sterically less demanding methyl substituents. This rigidification limits the distortion of the complex in the emissive excited-state, causing a decrease of the nonradiative relaxation rate by one order of magnitude. Compared to Ru II polypyridines, the molecular distortions in the luminescent 3 MLCT state relative to the electronic ground state seem to be smaller in the Mo 0 complexes, presumably due to delocalization of the MLCT-excited electron over greater portions of the ligands. Temperature-dependent studies indicate that thermally activated nonradiative relaxation via metal-centered excited states is more significant in these homoleptic Mo 0 tris(diisocyanide) complexes than in [Ru(2,2 -bipyridine) 3 ] 2+ . complexes with monodentate arylisocyanide ligands are very strong photoreductants, capable, for example, of reducing anthracene to its radical anion form. Many different kinds of metal complexes with isocyanide ligands have been explored over the past few decades [11][12][13][14][15], but metals with the d 6 or d 10 electron configurations are unique in their ability to show luminescence from a 3 MLCT excited state.Whilst structurally more flexible, multidentate isocyanide chelate ligands had been known for some time [16], we found that chelating diisocyanide ligands based on a m-terphenyl backbone permit the synthesis of homoleptic tris(diisocyanide) complexes of Cr 0 and Mo 0 that luminesce from 3 MLCT excited states (Figure 1) [17]. The molecular and the electronic structures of these compounds are reminiscent of Fe II and Ru II polypyridine complexes, which have been investigated extensively in the past. Until now, no convincing case of steady-state MLCT luminescence from a Fe II complex has been reported despite significant advances in extending their 3 MLCT lifetimes in recent years [18][19][20][21][22][23]; hence, our Cr 0 complex currently seems to be the only example of a first-row d 6 -metal complex showing MLCT luminescence in solution at room temperature under steady-state photo-irradiation [24]. The Mo 0 diisocyanide complexes are not only emissive, but they can furthermore be employed in photoredox catalysis of thermodynamically challenging reductions, which cannot be performed with more widely known photoreductants such as fac-[Ir(ppy) 3 ] (ppy = 2-phenylpyridine) [25]. Thus, the Mo 0 diisocyanide complexes represent Earth-abundant alternatives to precious-...

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Section: Resultssupporting

confidence: 81%

Section: Resultsmentioning

confidence: 77%

Section: Resultsmentioning

confidence: 99%

“…τ −1 = k r + k nr (1) 2+ 3,4 0.83 10.6 1 In toluene. 2 Weighted average of lifetime values (τ) used for the calculation (0.85 × 1110 ns + 0.15 × 2330 ns) [27]. 3 In acetonitrile.…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 92%

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Excited-State Relaxation in Luminescent Molybdenum(0) Complexes with Isocyanide Chelate Ligands

Herr

Wenger

2020

Inorganics

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Photophysics of Perylene Diimide Dianions and Their Application in Photoredox Catalysis

Wenger

2021

Angewandte Chemie

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The two-electron reduced forms of perylene diimides (PDIs) are luminescent closed-shell species whose photochemical properties seem underexplored. Our proof-of-concept study demonstrates that straightforward(single) excitation of PDI dianions with green photons provides an excited state that is similarly or more reducing than the muchshorter-lived excited states of PDI radical monoanions,w hicha re typically accessible after biphotonic excitation with blue photons. Thermodynamically demanding photocatalytic reductive dehalogenations and reductive CÀOb ond cleavage reactions of lignin model compounds have been performed using sodium dithionite acts as ar eductant, either in aqueous solution or in biphasic water-acetonitrile mixtures in the presence of aphase transfer reagent. Our work illustrates the concept of multielectron reduction of ap hotocatalyst by as acrificial reagent prior to irradiation with low-energy photons as am eans of generating very reactive excited states.

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Efficient Triplet‐Triplet Annihilation Upconversion Sensitized by a Chromium(III) Complex via an Underexplored Energy Transfer Mechanism

et al. 2022

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Sensitized triplet‐triplet annihilation upconversion (sTTA‐UC) mainly relies on precious metal complexes thanks to their high intersystem crossing (ISC) efficiencies, excited state energies, and lifetimes, while complexes of abundant first‐row transition metals are only rarely utilized and with often moderate UC quantum yields. [Cr(bpmp)2]3+ (bpmp=2,6‐bis(2‐pyridylmethyl)pyridine) containing earth‐abundant chromium possesses an absorption band suitable for green light excitation, a doublet excited state energy matching the triplet energy of 9,10‐diphenyl anthracene (DPA), a close to millisecond excited state lifetime, and high photostability. Combined ISC and doublet‐triplet energy transfer from excited [Cr(bpmp)2]3+ to DPA gives 3DPA with close‐to‐unity quantum yield. TTA of 3DPA furnishes green‐to‐blue UC with a quantum yield of 12.0 % (close to the theoretical maximum). Sterically less‐hindered anthracenes undergo a [4+4] cycloaddition with [Cr(bpmp)2]3+ and green light.

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Long-Lived, Strongly Emissive, and Highly Reducing Excited States in Mo(0) Complexes with Chelating Isocyanides

Cited by 81 publications

References 119 publications

Excited-State Relaxation in Luminescent Molybdenum(0) Complexes with Isocyanide Chelate Ligands

Excited-State Relaxation in Luminescent Molybdenum(0) Complexes with Isocyanide Chelate Ligands

Photophysics of Perylene Diimide Dianions and Their Application in Photoredox Catalysis

Efficient Triplet‐Triplet Annihilation Upconversion Sensitized by a Chromium(III) Complex via an Underexplored Energy Transfer Mechanism

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