The Carbene Cannibal: Photoinduced Symmetry-Breaking Charge Separation in an Fe(III) N-Heterocyclic Carbene.
Nidhi KaulReiner LomothPublished in: Journal of the American Chemical Society (2021)
Photoinduced symmetry-breaking charge separation (SB-CS) processes offer the possibility of harvesting solar energy by electron transfer between identical molecules. Here, we present the first case of direct observation of bimolecular SB-CS in a transition metal complex, [FeIIIL2](PF6) (L = [phenyl(tris(3-methylimidazol-1-ylidene))borate]-). Photoexcitation of the complex in the visible region results in the formation of a doublet ligand-to-metal charge transfer (2LMCT) excited state (E0-0 = 2.13 eV), which readily reacts with the doublet ground state to generate charge separated products, [FeIIL2] and [FeIVL2]2+, with a measurable cage escape yield. Known spectral signatures allow for unambiguous identification of the products, whose formation and recombination are monitored with transient absorption spectroscopy. The unusual energetic landscape of [FeIIIL2]+, as reflected in its ground and excited state reduction potentials, results in SB-CS being intrinsically exergonic (ΔGCS° ∼ -0.7 eV). This is in contrast to most systems investigated in the literature, where ΔGCS° is close to zero, and the charge transfer driven primarily by solvation effects. The study is therefore illustrative for the utilization of the rich redox chemistry accessible in transition metal complexes for the realization of SB-CS.
Keyphrases
- electron transfer
- transition metal
- solar cells
- systematic review
- high resolution
- magnetic resonance
- liquid chromatography
- dna damage
- molecular dynamics
- ionic liquid
- gene expression
- molecular dynamics simulations
- oxidative stress
- dna repair
- contrast enhanced
- dna methylation
- brain injury
- atomic force microscopy
- aqueous solution
- quantum dots