Concept
Photochemistry
Photochemistry uses absorbed light to generate excited states, radicals or catalytic redox cycles that thermal reactions cannot reach at the same temperature.
Visible-light photoredox is now core undergraduate organic chemistry, and chain vs closed-cycle behaviour changes how you count photons.
Evidence
What the evidence shows
Drawn from 10 studies in this library. Each finding starts with a plain-language takeaway, then the denser detail. Supports means evidence for a finding; Challenges means evidence against a stated position; Qualifies marks scope with a short note on each study’s contribution. Challenged positions are labeled — they are not findings.
This library holds 10 empirical chemistry papers on photochemistry with isolated findings, rates or spectra rather than reviews.
First-generation donor–acceptor Stenhouse adducts with a small N-methyl substituent switch well in chloroform; kinetics split photoisomerisation from cyclisation.
Cyclometalated Pt(II) complexes trifluoromethylate unactivated alkenes in >82% yield under 450 nm LEDs by oxidatively quenching CF3I.
Ir(ppy)2(NacNac) photocatalysts with BIH hydrodehalogenate unactivated aryl bromides, chlorides, fluorides, and alkyl bromides, including with green light.
A visible-absorbing Eu(II) azacryptate, assembled in situ from EuCl3, ligand and Zn0, reductively couples benzyl chloride to 1,2-diphenylethane with an excited-state potential near −3 V.
Open questions
Tensions and limits
Some items are genuine disagreements on the same question. Others mark different assays, populations, or outcomes — limits on how far one study travels — not a forced fight between papers.
Quantum yield, wavelength and quencher identity vary widely; a 'photocatalyst' can be a chain initiator rather than a closed cycle.
- DASA photoswitches work in chloroform if N-methyl
- Platinum photoredox catalysts for trifluoromethylation
Study Role Design N Population Outcome DASA photoswitches work in chloroform if N-methyl Supports OtherSynthesis and photoswitching kinetics/fatigue of DASA photochromes 1–14 Molecular photochrome SAR — no sample N Donor–acceptor Stenhouse adduct photoswitches Photoswitching amplitude, kinetics, and fatigue related to substituents Platinum photoredox catalysts for trifluoromethylation Supports OtherBlue-LED photoredox trifluoromethylation catalyzed by cyclometalated Pt(II) complexes Synthetic photoredox catalysis — no sample N Alkenes and heteroarenes under Pt(II)/CF3I photoredox conditions Trifluoromethylation yields and oxidative-quenching mechanism
Common misconceptions
Photoredox always means one photon per product molecule.
Quantum yields above 1 show product-forming chains, not a closed photocatalytic cycle.
Exam-style questions
Short-answer questions that ask you to explain or compare, not recall.
What does photochemistry mean in this chemistry library?
Photochemistry uses absorbed light to generate excited states, radicals or catalytic redox cycles that thermal reactions cannot reach at the same temperature.
Name one empirical finding from the photochemistry papers.
First-generation donor–acceptor Stenhouse adducts with a small N-methyl substituent switch well in chloroform; kinetics split photoisomerisation from cyclisation.
What is a limit of photochemistry evidence here?
Quantum yield, wavelength and quencher identity vary widely; a 'photocatalyst' can be a chain initiator rather than a closed cycle.
The studies
10 studies in this library bear on Photochemistry, ordered by citations. The first 8 are shown.
- Photoredox reactions that run as radical chains
Quantum yields of 44, 77, and 18 show product-forming chains—not a closed photocatalytic cycle of Φ ≤ 1—in three visible-light reactions.
- PQ and water oxy-trifluoromethylate enynes
Sunlight-excited phenanthrenequinone turns Langlois’ CF3SO2Na into CF3· and uses water as the oxygen atom to build CF3 benzofurans, benzothiophenes and indoles.
- Platinum photoredox catalysts for trifluoromethylation
Cyclometalated Pt(II) complexes trifluoromethylate unactivated alkenes in >82% yield under 450 nm LEDs by oxidatively quenching CF3I.
- DASA photoswitches work in chloroform if N-methyl
First-generation donor–acceptor Stenhouse adducts with a small N-methyl substituent switch well in chloroform; kinetics split photoisomerisation from cyclisation.
- Strongly reducing Ir photoredox on aryl chlorides
Ir(ppy)2(NacNac) photocatalysts with BIH hydrodehalogenate unactivated aryl bromides, chlorides, fluorides, and alkyl bromides, including with green light.
- Green-light ATRP that tolerates open air
Eosin Y plus a copper ATRP catalyst polymerizes OEOMA under green light in open vials, giving low dispersity even at 1000 rpm stirring.
- Eu(II) cryptate photocatalyzes bibenzyl coupling
A visible-absorbing Eu(II) azacryptate, assembled in situ from EuCl3, ligand and Zn0, reductively couples benzyl chloride to 1,2-diphenylethane with an excited-state potential near −3 V.
- ML and high-throughput screens find organic H2 photocatalysts
Screening 572 then 96 organic molecules under identical HER conditions, plus ML, uncovered unexpected molecular photocatalysts rivaling conjugated polymers.
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- Benzaldehyde photoredox heteroarylates amides and ethers
Household CFL light plus benzaldehyde and APS couples heteroarene C–H bonds to amide/ether α-C–H positions without a metal photocatalyst.
- Slow photogenerated Rh–H prefers aldehydes
Proflavine plus a Cp*Rh mediator makes dilute Rh(III)–H that reduces aldehydes while ketones wait, unlike fast formate hydride transfer.
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Change log
What changed
Dated edits to this page's evidence: studies added or removed from a claim, claims added or withdrawn, and new explanations tagged here. Rewordings are not listed.
- Concept page published