Photochemistry
Photoredox reactions that run as radical chains
Open access · cc by · source: Europe PMC
Quantum yields of 44, 77, and 18 show product-forming chains—not a closed photocatalytic cycle of Φ ≤ 1—in three visible-light reactions.
How this study connects
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- Quantum yields of 44 and 77 say these photoredox reactions run radical chains
This paper informs this development.
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Photoredox reactions that run as radical chains
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The Diels–Alder photoredox reaction has Φ = 44.
from these data, we calculate a quantum yield value of Φ = 44.
A second reaction has Φ = 77.
we calculated a quantum yield of Φ = 77, again demonstrating that product formation is dominated by a chain process.
Key findings
Φ = 44 (Diels–Alder; chain length ~41), Φ = 77 for a [2+2] (chain length Φ/Q = 135), and Φ = 18 for α-alkylation (vs 0.49 in a prior aerobic report). Φ ≫ 1 requires chains; light/dark experiments cannot disprove them.
Methodology
Authors measured 436 nm quantum yields against ferrioxalate (Φ = 1.01; flux 6.67×10−10 E s−1), combined them with luminescence quenching, and compared light/dark experiments on a radical-cation Diels–Alder, a radical-anion [2+2], and an α-alkylation.
Limitations
Not every photoredox reaction is a chain; the authors warn against over-generalizing, and aerobic vs N2 conditions change observed Φ.
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