NewIr Phenox O-PC™
Phenoxazine photocatalysts (Phenox O-PC™) are some of the strongest reducing visible light PCs available.1 Here are the ranges of photo and electrochemical properties for phenoxazine PC derivatives:
|Excited state redox potential||Eo(2PC+/1PC*) = -1.5V to -1.9V vs. SCE|
|Ground state oxidation potential||E1/2(2PC●+/PC*) = 0.6V to 0.9V vs. SCE|
|Excited state energy||E (singlet) = 2.2 to 2.6 eV|
|λmax,abs||362 – 410 nm|
|εmax,abs||19,000 – 37,000 M-1cm-1|
Phenoxazine PCs can be tuned for long excited state lifetimes, high triplet yields, and redox reversibility, properties advantageous for photocatalysis.2,3 In the case of Phenox O-PCTM A0202, it has τ(triplet) = 480 µs, φ(triplet) = 91%, and highly reversible cyclic voltammetry.2 Phenoxazine PCs have properties similar to the well-known precious metal Irppy3 [Eo(IrIV/IrIII*) = -1.73 V vs. SC;, E1/2(IrIV/IrIII) = 0.77 V vs. SCE; E(triplet) = 2.50 eV]; thus, phenoxazine PCs have been demonstrated as an effective drop-in replacement for Irppy3 in many cases and even outperforming Irppy3 in some applications.
Phenoxazine PCs are strong excited state reductants capable of reducing alkyl and aryl halides via an electron transfer mechanism. The alkyl radicals formed can partake in substitution or addition reactions on unsaturated vinyl or aromatic groups e.g., atom transfer radical polymerization, atom transfer radical addition and trifluoromethylation.1,2 This class of PCs can also activate Ni co-catalyst for C-N, C-S, C-O and C-C aryl cross-coupling reactions.2,4 In the case of C-N cross-coupling, spectroscopic evidence suggests that phenoxazine PC activates a Ni-amine co-catalyst via an energy transfer mechanism.5 Additionally, these PCs have been demonstrated in solar fuel generation converting CO2 to methane, thus closing the carbon cycle.6
1. Pearson, R. M.; Lim, C.-H.; McCarthy, B. G.; Musgrave, C. B.; Miyake, G. M., Organocatalyzed Atom Transfer Radical Polymerization Using N-Aryl Phenoxazines as Photoredox Catalysts. J. Am. Chem. Soc. 2016, 138, 11399.
2. Du, Y.; Pearson, R. M.; Lim, C.-H.; Sartor, S. M.; Ryan, M. D.; Yang, H.; Damrauer, N. H.; Miyake, G. M., Strongly Reducing, Visible-Light Organic Photoredox Catalysts as Sustainable Alternatives to Precious Metals. Chem. Eur. J. 2017, 23, 10962.
3. McCarthy, B. G.; Pearson, R. M.; Lim, C.-H.; Sartor, S. M.; Damrauer, N. H.; Miyake, G. M., Structure–Property Relationships for Tailoring Phenoxazines as Reducing Photoredox Catalysts. J. Am. Chem. Soc. 2018, 140, 5088.
4. Escobar, R. A.; Johannes, J. W., A Unified and Practical Method for Carbon–Heteroatom Cross-Coupling using Nickel/Photo Dual Catalysis. Chem. Eur. J. 2020, 26, 5168.
5. Kudisch, M.; Lim, C.-H.; Thordarson, P.; Miyake, G. M., Energy Transfer to Ni-amine Complexes in Dual Catalytic, Light-driven C–N Cross-coupling Reactions. J. Am. Chem. Soc. 2019, 141, 19479.
6. Rao, H.; Lim, C.-H.; Bonin, J.; Miyake, G. M.; Robert, M., Visible-Light-Driven Conversion of CO2 to CH4 with an Organic Sensitizer and an Iron Porphyrin Catalyst. J. Am. Chem. Soc 2018, 140, 17830.