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Substituent effects on dynamics at conical intersections: alpha,beta-enones.
A M D Lee1, J D Coe, S Ullrich
1Steacie Institute for Molecular Sciences, National Research Council, Ottawa, ON, Canada.
The Journal of Physical Chemistry. A
|November 8, 2007
Summary
Methyl substitution significantly impacts alpha,beta-enone relaxation dynamics. While S2 state decay is similar, S1 state relaxation and product branching ratios vary based on methyl group position, suggesting dynamical factors influence conical intersection passage.
Area of Science:
- Photochemistry
- Molecular Dynamics
- Quantum Chemistry
Background:
- Alpha,beta-enones are crucial in photochemistry.
- Understanding their excited-state dynamics is key to controlling photochemical reactions.
Purpose of the Study:
- Investigate methyl substitution effects on the electronic dynamics of alpha,beta-enones.
- Elucidate the relaxation pathways following excitation to the S2(pipi*) state.
Main Methods:
- Femtosecond time-resolved photoelectron spectroscopy.
- High-level ab initio theoretical calculations.
Main Results:
- Excited enones rapidly access conical intersections, leading to S1(npi*) and then ground state relaxation.
- S2 decay times show minor variations, but S1 relaxation rates and product branching ratios are sensitive to methyl group position.
- Ab initio calculations did not fully explain observed relaxation variations.
Conclusions:
- Methyl substitution position critically influences S1 state relaxation rates and product distributions in alpha,beta-enones.
- Dynamical factors, not just static geometry, likely govern the efficiency of passage through S1/S0 conical intersections.
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