Elucidating the Ultrafast Dynamics of Photoinduced Charge Separation in Metalloporphyrin-Fullerene Dyads Across the Electromagnetic Spectrum

Abstract

Metalloporphyrins are prominent building blocks in the synthetic toolbox of advanced photodriven molecular devices. When the central ion is paramagnetic, the relaxation pathways within the manifold of excited states are highly intricate so that unravelling the intramolecular energy and electron transfer processes is usually a very complex task. This fact is critically hampering the development of applications based on the enhanced coupling offered by the electronic exchange interaction. In this work, the dynamics of charge separation in a copper porphyrin-fullerene are studied with several complementary spectroscopic tools across the electromagnetic spectrum (from near infra-red to X-ray wavelengths), each of them providing specific diagnostics. Correlating the various rates clearly demonstrates that the lifetime of the photoinduced charge-separated state exceeds by about 10 fold that of the isolated photoexcited Cu II porphyrin. As revealed by the spectral modifications in the XANES region, this stabilization is accompanied by a transient change in covalency around the Cu II center, which is induced by an enhanced interaction with the C 60 moiety. This experimental finding is further confirmed by state-of-the art calculations using DFT and TD-DFT including dispersion effects that explain the electrostatic and structural origins of this interaction, as the Cu II P cation becomes ruffled and approaches closer to the fullerene in the charge-separated state. From a methodological point of view, these results exemplify the potential of multielectron excitation features in transient X-ray spectra as future diagnostics of sub-femtosecond electronic dynamics. From a practical point of view, this work is paving the way for elucidating out-ofequilibrium electron transfer events coupled to magnetic interaction processes on their intrinsic time-scales.

Mn–O–O Electron Spin Flip Mechanism Triggered by the Visible-Light Irradiation for the Generation of an Active Mn(V)–Oxo Complex from O2: Insight from Density Functional Calculations

“…As is well-known, transition-metal complexes have structural diversity ,,− and can form active oxygen species of M x –O 2 (M = Fe, Co, Ni, Cu, Mn and x = 1 or 2). − Recently, the Goldberg group first reported that the high-valent Mn­(V)–oxo corrolazine complex can be generated by the direct conversion of Mn­(III)–corrolazine complex with O 2 as the oxidant under the visible-light irradiation. Moreover, the photocatalytic oxidation of substrate can be performed using O 2 as the oxidant with the Mn­(III)–corrolazine complex functioning as an active photocatalyst under photoreaction conditions, where a Mn­(V)–oxo corrolazine complex was formed, which can rapidly oxidize the substrate with the concomitant regeneration of the Mn­(III)–corrolazine complex.…”

Mapping the Initial Stages of a Protective Pathway that Enhances Catalytic Turnover by a Lytic Polysaccharide Monooxygenase

“…Copper K-edge HERFD–XAS spectra (collected at 10 K to avoid significant photoreduction of the sample, Figure S48) of samples trapped at 100 ms, and subsequently annealed to 150 K, revealed an edge position at 8985.8(3) eV, consistent with a sample that is principally in the Cu II oxidation state . An intense rising-edge feature at 8981.9(3) eV is also observed, likely to be either a Cu II shakedown transition often observed in the K-edge XANES spectra of Cu II species, or a 1s–4p transition that is observed in the equivalent Cu I form of the enzyme at the same position. The latter could arise from partial photoreduction of the sample or any unreacted Cu I form of the enzyme remaining in the sample .…”

The histidine-brace active site of a copper monooxygenase is redox active and forms part of an in-built enzyme repair mechanism

“…Copper K-edge HERFD-XAS spectra (collected at 10 K to avoid signi cant photoreduction of the sample, Supplementary information) of samples trapped at 100 and 380 ms, and subsequent annealing through a temperature range of 150 to 250 K, revealed in all cases an edge position at 8985.8(3) eV, consistent with a sample that is principally in the Cu II oxidation state 19 . An intense rising-edge feature at 8981.9 (3) eV is also observed, likely to be either a Cu II shakedown transition often observed in the K-edge XANES spectra of Cu II species 27 , or a 1s-4p transition that is observed in the equivalent Cu I form of the enzyme at the same position, which could arise from partial photoreduction of the sample 19 . In the samples trapped at 100 ms, which had been annealed to 150 K and 250 K, two weak pre-edge features at 8977.7(3) eV and 8979.2(3) eV were also observed (Fig.…”