Inversion of donor–acceptor roles in photoinduced intervalence charge transfers

Aramburu-Trošelj, Bruno M.; Oviedo, Paola S.; Ramírez‐Wierzbicki, Ivana; Baraldo, Luis M.; Cadranel, Alejandro

doi:10.1039/c9cc03483h

Cited by 22 publications

(25 citation statements)

References 49 publications

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“…Based on these interesting excited states, we suggest that an internal electron donor could function as a photoreductant in lieu of aggressive reductants such as NaEt 3 BH or Na(Hg). Electronic coupling in excited states is an area of continued interest and exploration and the easily accessible charge transfer in this system yields only a partial hole (see theory section) at ferrocene, which may reveal interesting properties…”

Section: Discussionmentioning

confidence: 99%

“…44b Based on these interesting excited states, we suggest that an internal electron donor could function as a photoreductant in lieu of aggressive reductants such as NaEt 3 BH or Na(Hg). Electronic coupling in excited states is an area of continued interest and exploration 58 and the easily accessible charge transfer in this system yields only a partial hole (see theory section) at ferrocene, which may reveal interesting properties Spectroelectrochemistry. In accord with the CV experiments, free Fc 2 PDI is not stable in its mixed valent state and cannot be observed by spectroelectrochemistryconstant potential electrolysis continues until 2e − are removed from the molecule.…”

Section: ■ Discussionmentioning

confidence: 99%

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Bis-Ferrocenyl-Pyridinediimine Trinuclear Mixed-Valent Complexes with Metal-Binding Dependent Electronic Coupling: Synthesis, Structures, and Redox-Spectroscopic Characterization

et al. 2020

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A family of metal dichloride complexes having a bis-ferrocenyl-substituted pyridinediimine ligand was systematically synthesized ((Fc2PDI)MCl2, M = Mg, Zn, Fe, and Co) and characterized crystallographically, spectroscopically, electrochemically, and computationally. Electronic coupling between the ligand ferrocene units is switched on upon binding to a MCl2 fragment, as evidenced by both sequential oxidation of the ferrocenes in cyclic voltammetry (ΔE ox ≈ 200 mV) and by Inter-Valence Charge Transfer electronic excitations in the near IR. Additionally, UV–vis spectra are used to directly observe orbital mixing between the ferrocenyl units and the imine π system since breaking of the orbital symmetry results in allowed transitions (ϵ = 2800 M–1cm–1 vs ϵ ≈ 200 M–1cm–1 in free ferrocene) as well as broadening and red-shifting of the ferrocenyl transitionsindicating organic character in formerly pure metal-centered transitions. DFT analysis reveals that interaction between the ferrocenes and the MCl2 fragment is small and suggests that communication is mediated by better energy matching between the ferrocene and organic π* orbitals upon coordination, allowing superexchange coupling through the LUMO. Furthermore, single crystal diffraction data obtained from oxidation of one and both ferrocenes show distortions, introducing the empty d xy /d x2‑y2 orbitals into the secondary coordination sphere of the MCl2 fragment. Such structural rearrangements are infrequent in ferrocenyl mixed-valent compounds, and implications for catalysis as well as electronic communication are discussed.

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Section: Discussionmentioning

confidence: 99%

Section: ■ Discussionmentioning

confidence: 99%

Bis-Ferrocenyl-Pyridinediimine Trinuclear Mixed-Valent Complexes with Metal-Binding Dependent Electronic Coupling: Synthesis, Structures, and Redox-Spectroscopic Characterization

et al. 2020

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“…S3). This differential spectrum lacks any strong photoinduced absorptions in the NIR, which are usually associated with photoinduced intervalence charge transfers (PIIVCT) as observed in other mulitmetallic assemblies (30). We assign this absence to the orientation of the ruthenium dπ(t 2g ) orbital bearing the excited hole in this MLCT excited state, that is orthogonal to the intermetallic z axis (17,31).…”

Section: Resultsmentioning

confidence: 77%

“…The former indicates the loss of ground state population upon photoexcitation. The latter corresponds to a PIIVCT within the {RuRu} moiety in the photoexcited trimetallic complex and indicates strong metal-metal electronic communication (30). Importantly, previous…”

Section: Resultsmentioning

confidence: 89%

Bifurcation of excited state trajectories toward energy transfer or electron transfer directed by wave function symmetry

Oviedo

Baraldo

Cadranel

2021

Proc. Natl. Acad. Sci. U.S.A.

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This work explores the concept that differential wave function overlap between excited states can be engineered within a molecular chromophore. The aim is to control excited state wave function symmetries, so that symmetry matches or mismatches result in differential orbital overlap and define low-energy trajectories or kinetic barriers within the excited state surface, that drive excited state population toward different reaction pathways. Two donor–acceptor assemblies were explored, where visible light absorption prepares excited states of different wave function symmetry. These states could be resolved using transient absorption spectroscopy, thanks to wave function symmetry-specific photoinduced optical transitions. One of these excited states undergoes energy transfer to the acceptor, while another undertakes a back-electron transfer to restate the ground state. This differential behavior is possible thanks to the presence of kinetic barriers that prevent excited state equilibration. This strategy can be exploited to avoid energy dissipation in energy conversion or photoredox catalytic schemes.

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“…One of them (blue curve in Figure ) shows the bleached GSMLCT and GSIVCT absorptions at 21 300 and 8600 cm –1 , respectively. Additionally, it presents broad photoinduced absorptions between 14 000 and 19 000 cm –1 , which correspond to radical anion-centered π* ← π* transitions and dπ(Ru) ← π* photoinduced LMCT bands, involving both the radical anion and the NC bridge. ,, Its electronic configuration can be formally described as {(tpy· – )Ru III –NC-Os III }. The presence of the GSIVCT bleach reveals that the excited hole lies in a chromophore-centered orbital involved in the ground-state mixed-valence interactions, that is, a dπ z orbital extending along the bimetallic core.…”

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confidence: 99%

Wave-Function Symmetry Control of Electron-Transfer Pathways within a Charge-Transfer Chromophore

Aramburu-Trošelj

Ramírez‐Wierzbicki

Scarcasale

et al. 2020

J. Phys. Chem. Lett.

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Despite a diverse manifold of excited states available, it is generally accepted that the photoinduced reactivity of charge-transfer chromophores involves only the lowest-energy excited state. Shining a visible-light laser pulse on an aqueous solution of the chromophore-quencher [Ru(tpy)(bpy)(μNC)OsIII(CN)5]− assembly (tpy = 2,2′;6,2''-terpyridine and bpy = 2,2′-bipyridine), we prepared a mixture of two charge-transfer excited states with different wave-function symmetry. We were able to follow, in real time, how these states undergo separate electron-transfer reaction pathways. As a consequence, their lifetimes differ in 3 orders of magnitude. Implicit are energy barriers high enough to prevent internal conversion within early excited-state populations, shaping isolated electron-transfer channels in the excited-state potential energy surface. This is relevant not only for supramolecular donor/acceptor chemistry with restricted donor/acceptor relative orientations. These energy barriers provide a means to avoid chemical potential dissipation upon light absorption in any molecular energy conversion scheme, and our observations invite to explore wave-function symmetry-based strategies to engineer these barriers.

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Inversion of donor–acceptor roles in photoinduced intervalence charge transfers

Abstract: Upon MLCT photoexcitation, {(tpy)Ru} becomes the electron acceptor in the mixed valence {(tpy˙−)RuIII−δ-NC-MII+δ} moiety, reversing its role as the electron donor in the ground-state mixed valence analogue.

Cited by 22 publications

References 49 publications

Bis-Ferrocenyl-Pyridinediimine Trinuclear Mixed-Valent Complexes with Metal-Binding Dependent Electronic Coupling: Synthesis, Structures, and Redox-Spectroscopic Characterization

Bis-Ferrocenyl-Pyridinediimine Trinuclear Mixed-Valent Complexes with Metal-Binding Dependent Electronic Coupling: Synthesis, Structures, and Redox-Spectroscopic Characterization

Bifurcation of excited state trajectories toward energy transfer or electron transfer directed by wave function symmetry

Wave-Function Symmetry Control of Electron-Transfer Pathways within a Charge-Transfer Chromophore

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