Here we report light induced electron transfer (ET) dynamics from an organic photosensitizer (3,7-di([1,1′-biphenyl]-4-yl)-10-(naphthalen-1-yl)-10H-phenoxazine, Phen2) to an iron porphyrin catalyst (Fe(III) meso-tetra(4-N,N,N-trimethylanilinium)porphine pentachloride, FeIII-p-TMA) in the presence of sacrificial electron donors using time-resolved Fe K-edge x-ray absorption near-edge structure spectroscopy. Upon 400 nm excitation, both singlet and triplet states of Phen2 enable to transfer an electron to FeIII-p-TMA (bimolecular ET rate: ~6.3 ns and ~270 ns, respectively) resulting in its geometry change from square pyramid to square planar. The fast ET seems to stem from Van der Waals interaction among catalysts. Interestingly, the intermolecular ET from Phen2 in singlet to Fe-p-TMA seems to be favored than intersystem crossing of Phen2. The formation of FeII-p-TMA maximizes in 1 µs and it relaxes via two states having lifetime of ~ 3 µs and ~ 40 µs, which are sufficiently long for further reduction to Fe0.

Probing electron transfer dynamics of an iron porphyrin photocatalyst for CO2 reduction using time-resolved x-ray absorption spectroscopy

ACS Spring 2022

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