A photoinduced mixed valence photoswitch

Cotic, Agustina; Cerfontaine, Simon; Slep, Leonardo D.; Elias, Benjamin; Troian‐Gautier, Ludovic; Cadranel, Alejandro

doi:10.1039/d2cp01791a

Cited by 11 publications

(33 citation statements)

References 71 publications

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“…Similar PIIVCT were also observed for 3 MLCT(Lp). 15 DFT and TD-DFT calculations of the lowest triplet state of Dm (Figures S3-S4, Tables S1-S2, and details in the SI) were consistent with our experimental interpretation.…”

Section: Resultssupporting

confidence: 86%

“…The longest lifetime and its associated differential spectrum matched those obtained for the emissive 3 MLCT(Lm), which also include bridging ligand radical anions according to spectroelectrochemistry (Figure S2 and details in the SI). 15,21 This excited state also featured a photoinduced absorption at 8400 cm -1 (1190 nm) assigned to a photoinduced intervalence charge transfer (PIIVCT) involving the two Ru ions, originating in a {Ru III- (Lm •-)Ru II+ } electronic configuration for 3 MLCT(Lm). Similar PIIVCT were also observed for 3 MLCT(Lp).…”

Section: Resultsmentioning

confidence: 97%

“…Therefore, poor excited-state electronic coupling scenarios, where high kinetic barriers mediate IC/VR (Figure 1, bottom), must be explored to realize anti-Kasha photochemistry and anti-dissipative energy conversion. Observations involving a variety of intramolecular donor/bridge/acceptor processes, ranging from singlet fission to ground-and excited-state intervalence charge transfers, [6][7][8][9][10][11][12][13][14][15] suggest that the topology of the bridge can be exploited to modulate excited-state electronic coupling. 16,17 Prototypical polynuclear ruthenium polypyridines 18,19 provide an ideal platform for these studies because their excited states have clear spectroscopic handles, with well-defined long-lived metal-to-ligand charge transfer (MLCT) transitions and they are widely used in energy conversion schemes and photoredox catalysis.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, it was shown that Dp behaves as a typical Kasha chromophore. 15 The excited state behavior is dominated by lowest triplet state, which is an emissive Metal-to-Ligand Charge Transfer 3 MLCT(Lp) state. It includes a bridging ligand radical anion according to spectroelectrochemistry.…”

Section: Introductionmentioning

confidence: 99%

“…It includes a bridging ligand radical anion according to spectroelectrochemistry. 15 Only very minor differential spectral changes were observed from the pico-to the microsecond timescale by transient absorption spectroscopy (TAS), highlighting that the changes of excited-state electronic configuration associated to IC occurred on the subpicosecond timescale. Upon excitation and intersystem crossing, vibrationally hot 3 MLCT(Lp) relaxed to the thermally-equilibrated 3 MLCT(Lp) in less than 10 ps, typical for vibrational relaxation processes in [Ru(bpy)3] 2+ and other ruthenium polypyridine chromophores.…”

Section: Introductionmentioning

confidence: 99%

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Anti-dissipative strategies towards more efficient solar energy conversion

Cotic

Cerfontaine²,

Slep

et al. 2022

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In natural and artificial photosynthesis, light absorption and catalysis are separate processes linked together by exergonic electron transfer. This leads to free energy losses between the initial excited state, formed after light absorption, and the catalytic center formed after the electron transfer cascade. Additional deleterious processes, such as internal conversion and vibrational relaxation, also dissipate as much as 20-30 % of the absorbed photon energy. Minimization of these energy losses, a holy-grail in solar energy conversion and solar fuels production, is a challenging task, because excited states are usually strongly coupled which results in negligible kinetic barriers and very fast dissipation. Here we show that topological control of oligomeric {Ru(bpy)3} chromophores resulted in small excited-state electronic couplings, leading to activation barriers for internal conversion of around 2000 cm–1 and effectively slowing down dissipation. Two types of excited states are populated upon visible light excitation, i.e. a bridging-ligand centered metal-to-ligand charge transfer (MLCTLm), and a 2,2’-bipyridine-centered MLCT (MLCTbpy), which lies 800-1400 cm–1 higher in energy. As a proof-of-concept, bimolecular electron transfer with tri-tolylamine as electron donor was performed, which mimics catalyst activation by sacrificial electron donors in typical photocatalytic schemes. Both excited states were efficiently quenched by tri-tolylamine and produced the corresponding bpy•– and Lm•– centered reduced complexes, as confirmed by transient absorption spectroscopy. This efficiently generated two distinct reduced photosensitizers with different reducing abilities, i.e. –0.93 V and –0.79 V vs NHE for bpy•– and Lm•–, respectively. Hence, this novel strategy not only allows to trap higher energy excited states, before internal conversion and vibrational relaxation set in, saving between 110 and 170 meV and but also leads in fine to 140 meV more potent reductant for energy conversion schemes and solar fuels production. These results lay the first stone for anti-dissipative energy conversion schemes which, in bimolecular electron transfer reactions, harnesses the excess energy saved by controlling dissipative conversion pathways.

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Section: Resultssupporting

confidence: 86%

Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Anti-dissipative strategies towards more efficient solar energy conversion

Cotic

Cerfontaine²,

Slep

et al. 2022

Preprint

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The Excited‐State Creutz–Taube Ion

2022

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The excited-state version of the Creutz-Taube ion was prepared via visible light excitation of [(NH 3 ) 5 Ru II (μ-pz)Ru II (NH 3 ) 5 ] 4 + . The resulting excited state is a mixed valence {Ru III-δ (μ-pz *À )Ru II + δ } transient species, which was characterized using femtosecond transient absorption spectroscopy with vis-NIR detection. Very intense photoinduced intervalence charge transfers were observed at 7500 cm À 1 , revealing an excited-state electronic coupling element H DA = 3750 cm À 1 . DFT calculations confirm a strongly delocalized excited state. A notable consequence of strong electron delocalization is the nanosecond excited state lifetime, which was exploited in a proof-of-concept intermolecular electron transfer. The excited-state Creutz-Taube ion is established as a reference, and demonstrates that electron delocalization in the excited state can be leveraged for artificial photosynthesis or other photocatalytic schemes based on electron transfer chemistry.

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