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Updated: Apr 28, 2026
09:33
Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
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Inverted substrate preferences for photochemical heterolysis arise from conical intersection control
Alexander T Buck1, Christie L Beck, Arthur H Winter
1Department of Chemistry, Iowa State University , 2101d Hach Hall, Ames, Iowa 50011, United States.
Journal of the American Chemical Society
|June 10, 2014
Summary
Researchers explored how molecular structure affects chemical reactions in excited states. They found that unstabilized carbocations favor photochemical reactions, while stabilized ones favor thermal reactions due to conical intersection control.
Area of Science:
- Photochemistry
- Theoretical Chemistry
- Organic Chemistry
Background:
- Understanding thermal heterolysis of carbon-leaving group (C-LG) bonds is established.
- General models connecting structure to reactivity for excited-state heterolysis are lacking.
Purpose of the Study:
- Investigate structure-reactivity relationships in excited-state heterolysis.
- Explore the role of conical intersections in photoheterolysis reactions.
Main Methods:
- Computational chemistry approach using CASSCF (Complete Active Space Self-Consistent Field) calculations.
- Conical intersection searches were performed on representative systems undergoing photoheterolysis.
Main Results:
- Unstabilized carbocations exhibit low-energy conical intersections, favoring photochemical reactions.
- Stabilized carbocations show high-energy conical intersections, favoring thermal reactions.
- A shift from transition-state control (thermal) to conical intersection control (photochemical) explains reactivity inversions.
Conclusions:
- Conical intersections are crucial in controlling reactivity in photoheterolysis.
- The interplay between ground and excited state surfaces influences the formation of productive conical intersections.
- This study provides a framework for understanding excited-state heterolysis mechanisms.
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