Ultrafast transient IR spectroscopy and DFT calculations of ruthenium(<scp>ii</scp>) polypyridyl complexes

Sun, Qinchao; Dereka, Bogdan; Vauthey, Eric; Daku, Latévi Max Lawson; Hauser, Andreas

doi:10.1039/c6sc01220e

Cited by 68 publications

(100 citation statements)

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“…However, in Ru II polypyridine complexes there is usually additional nonradiative relaxation from the 3 MLCT via the 3 T 1g excited state (Figure 3b) [37,38]. Depending on ligand design [39], this metal-centered state can be energetically very close and nonradiative relaxation becomes very rapid, and this is the reason why [Ru(tpy) 2 ] 2+ (tpy = 2,2 :6 ,2"-terpyridine) is essentially non-emissive in solution at room temperature [40]. Conversely, when the 3 T 1g state is located energetically sufficiently above the 3 MLCT manifold, high luminescence quantum yields and long excited state lifetimes are achievable [41].…”

Section: Resultsmentioning

confidence: 99%

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: Resultsmentioning

confidence: 99%

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

Herr

Wenger

2020

Inorganics

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“…This horizontal displacement opensu pap athway for the 3 MLCT excited-state population to cross over ac ertain barrieri nto the 3 T 1g state, and from there onwards to the 1 A 1g ground state. [4] In [Ru(tpy) 2 ] 2 + (tpy = 2,2':6',2''-terpyridine), the 3 T 1g state is markedly lower than that in [Ru(bpy) 3 ] 2 + ,a nd this is the main reason why [Ru(tpy) 2 ] 2 + is essentially nonemissive at room temperature in fluid solution, whereas [Ru(bpy) 3 ] 2 + has ad ecent luminescence quantumy ield under such conditions. [5] The lower energy of the 3 T 1g state in [Ru(tpy) 2 ] 2 + is ad irect consequence of the weaker ligand field caused by tpy,r elative to bpy,due to smaller N-Ru-N angles.…”

Section: Commonalities and Differencesi Nt He Photophysics Of Ru II Amentioning

confidence: 99%

Is Iron the New Ruthenium?

Wenger

2019

Chemistry A European J

234

273

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Ruthenium complexes with polypyridine ligands are very popularc hoices for applications in photophysics and photochemistry,f or example, in lighting, sensing, solar cells, and photoredox catalysis. There is al ong-standing interest in replacing ruthenium with iron because ruthenium is rare and expensive, whereas iron is comparatively abundant and cheap.H owever,i ti sv ery difficult to obtain iron complexes with an electronic structure similart ot hat of ruthenium(II) polypyridines. The latter typicallyh ave al onglived excited state with pronounced charge-transferc haracter between the ruthenium metal and ligands. These metalto-ligand charge-transfer( MLCT) excited states can be luminescent, with typical lifetimesi nt he range of 100 to 1000 ns, and the electrochemical properties are drastically altered during this time. These properties make ruthenium(II) polypyridine complexes so well suited for the abovementioned applications. In iron(II) complexes, the MLCT states [a] Prof.

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“…For instance, in the extensively studied prototype Fe II molecule Fe II (bpy) 3 (bpy=2,2′‐bipyridine), the charge‐separated MLCT state deactivates on an ultrafast timescale into high‐spin MC states . Similar ultrafast transitions into 3 MC states have been observed and described for ruthenium sensitizer complexes . By destabilizing the MC scavenger states we, and other groups, have recently developed iron complexes with significantly slower deactivation of the MLCT states …”

Section: Introductionmentioning

confidence: 58%

“…[9,10] Similar ultrafast transitions into 3 MC states have been observed and described for ruthenium sensitizer complexes. [11][12][13] By destabilizing the MC scavenger states we,a nd other groups,h ave recently developed iron complexes with significantly slower deactivation of the MLCT states. [14][15][16][17][18][19][20][21] This makes the iron carbene complexes interesting as ap romising new class of photosensitizers, [22] with recently demonstrated capability to inject electrons efficiently into aT iO 2 substrate,a nd carry out bimolecular oxidation and reduction processes.…”

Section: Introductionmentioning

confidence: 99%

Hot Branching Dynamics in a Light‐Harvesting Iron Carbene Complex Revealed by Ultrafast X‐ray Emission Spectroscopy

et al. 2019

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Iron N‐heterocyclic carbene (NHC) complexes have received a great deal of attention recently because of their growing potential as light sensitizers or photocatalysts. We present a sub‐ps X‐ray spectroscopy study of an FeIINHC complex that identifies and quantifies the states involved in the deactivation cascade after light absorption. Excited molecules relax back to the ground state along two pathways: After population of a hot 3MLCT state, from the initially excited 1MLCT state, 30 % of the molecules undergo ultrafast (150 fs) relaxation to the 3MC state, in competition with vibrational relaxation and cooling to the relaxed 3MLCT state. The relaxed 3MLCT state then decays much more slowly (7.6 ps) to the 3MC state. The 3MC state is rapidly (2.2 ps) deactivated to the ground state. The 5MC state is not involved in the deactivation pathway. The ultrafast partial deactivation of the 3MLCT state constitutes a loss channel from the point of view of photochemical efficiency and highlights the necessity to screen transition‐metal complexes for similar ultrafast decays to optimize photochemical performance.

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Ultrafast transient IR spectroscopy and DFT calculations of ruthenium(ii) polypyridyl complexes

Abstract: TRIR spectroscopy identifies the low-energy ligand-field state in the relaxation cascade for ruthenium(ii) polypyridyl complexes.

Cited by 68 publications

References 50 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

Is Iron the New Ruthenium?

Hot Branching Dynamics in a Light‐Harvesting Iron Carbene Complex Revealed by Ultrafast X‐ray Emission Spectroscopy

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