Phenoxazine‐Sensitized CO₂‐to‐CO Reduction with an Iron Porphyrin Catalyst: A Redox Properties‐Catalytic Performance Study

Abstract

We have evaluated six phenoxazine derivatives as visible light photosensitizers for the photochemical reduction of CO2 to CO with an iron porphyrin catalyst in organic media. The phenoxazine core was functionalized with electron‐donating or ‐withdrawing groups to modify the photophysical properties. Both singlet and triplet excited state potentials of the sensitizers spanned several hundred mV range and the ground state oxidation potentials spanned 250 mV. We observed that no correlation can be established between the production of CO and the excited state potential of the phenoxazine, which determines the driving force for electron transfer to the catalyst. On the contrary, a clear correlation can be made between the oxidation potentials of the phenoxazine and the production of CO. This observation indicates that the process was limited by photosensitizer regeneration and highlights the fact that electron transfers not directly related to the catalyst activation could play a key role in homogeneous photocatalytic systems.

Porphyrins and phthalocyanines as biomimetic tools for photocatalytic H2production and CO2reduction

“…The same group in a recent report evaluated six phenoxazine derivatives as visible light photosensitizers for the photo-initiated CO 2 to CO reduction, using Fe-p-TMA as catalyst in CH 3 CN solution. 194 The photcatalytic studies demonstrated that the production of CO is strongly related to the oxidation potential of the Phen sensitizer. This unexpected result indicates that photosensitizer regeneration by the SED is the rate-limiting step of this catalytic system.…”

Mechanistic Insights into Photochemical CO2 Reduction to CH4 by a Molecular Iron–Porphyrin Catalyst

“…In such a CO 2 reduction system, the catalyst is reduced after gaining electrons from the oxidative/reductive quenching process of the excited photosensitizer to generate the catalytically active species. Apart from the noble metal complexes (i.e., Re, − Ru, − Rh, and Ir complexes − ), many non-noble transition metal complexes, such as Mn, − Fe, − Co, − Ni, − and Cu complexes, − have also been used in photochemical CO 2 reduction. Modifying the ligands from neutral to charged groups can stabilize the critical M–CO 2 and M–CO intermediates through noncovalent electrostatic interactions, thus promoting the CO 2 RR toward target products.…”

Defluorinative Alkylboration of Alkenes Enabled by Dual Photoredox and Copper Catalysis

“…[12b,17] We found that neither PhCF 3 1 a nor B 2 pin 2 /KOH showed significant quenching toward the excited state *PC-I, consistent with their redox potentials. [18] While the mixtures of 1 a/B 2 pin 2 (1 : 1) and 1 a/B 2 pin 2 /KOH (1 : 1 : 1) exhibited more significant quenching to *PC-I (K sv = 28.0 for the former and K sv = 58.0 for the latter) (see ESI for more 19 F NMR and UV/Vis Absorption Spectroscopic Studies). These results suggested that B 2 pin 2 /KOH could facilitate the challenging SET reduction of PhCF 3 and subsequent fluoride elimination process.…”