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When Light Challenges Heat: Mechanistic Insights Into a Reaction Competing With Cadogan Cyclisation in
Manuel Pedrón Laserna1,2, Ilaria Ciofini1, Piétrick Hudhomme3
1Chimie Paris Tech, CNRS, Institute of Chemistry for Life and Health Sciences, PSL University, Paris, France.
Visible light triggers unique reactions in nitrated perylenediimides (PDIs) with triphenylphosphine, unlike thermal conditions. This photochemical control unlocks new synthetic pathways by altering excited states.
Area of Science:
- Organic Photochemistry
- Sustainable Synthesis
- π-Conjugated Systems
Background:
- Visible-light photocatalysis offers sustainable synthetic routes.
- Photochemical reactivity of polycyclic aromatic hydrocarbons (PAHs) is underexplored.
- Perylenediimides (PDIs) possess desirable photophysical properties but limited understood light-induced transformations.
Purpose of the Study:
- Investigate the divergent thermal versus photochemical reactivity of bay-nitrated PDIs (PDI-NO2) with triphenylphosphine.
- Explore the mechanism of light-induced transformations in PDIs.
- Establish principles for controlling reaction pathways using visible light.
Main Methods:
- Comparative studies of thermal and visible-light-driven reactions.
- Wavelength-dependent photochemical experiments.
- Spectroscopic analysis and theoretical calculations (DFT) to elucidate reaction mechanisms.
Main Results:
- Visible light irradiation of PDI-NO2 with triphenylphosphine yields a novel bay-functionalized 1-(iminophosphorane)-12-hydroxy PDI derivative, distinct from the thermal Cadogan reaction product.
- Blue light was most effective for the photochemical transformation.
- Photoexcited PDI-NO2 exhibits strong reducing power, initiating nitro-to-nitroso conversion.
- Light enables access to charge-transfer and π-π* excited states, facilitating phosphine addition.
Conclusions:
- Visible light irradiation provides unprecedented control over PDI reactivity, enabling pathways inaccessible under thermal conditions.
- Orbital-selective excitation is a key principle for directing photochemical reactions in π-conjugated systems.
- This work expands the synthetic utility of PDIs and visible-light photocatalysis.
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