Reactivities of singlet oxygen: open-shell or closed-shell?

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Photochemistry

Background:

• Singlet oxygen is crucial in photochemistry.
• Understanding its reactivity is key for applications like photodynamic therapy.
• Excitation energy transfer (EET) and cycloaddition are important reactions involving singlet oxygen.

Purpose of the Study:

• To investigate the reactivity of singlet oxygen in cycloaddition and EET reactions.
• To analyze the role of open-shell (OS) and closed-shell (CS) components of singlet oxygen's degenerate state.
• To explore the applicability of the diabatic perspective to singlet fission.

Main Methods:

• Multistate density functional theory (MSDFT) was employed.
• Diabatic states were used to model the reactions.
• Calculations focused on the cycloaddition to anthracene and EET to a carotenoid.

Main Results:

• The closed-shell (CS) component of singlet oxygen's degenerate state exhibited higher reactivity.
• Strong diabatic couplings to product diabatic states influenced reactivity.
• The diabatic approach provided insights into reaction mechanisms.

Conclusions:

• The diabatic perspective offers a valuable framework for understanding singlet oxygen reactivity.
• This approach can be extended to other photochemical processes, including singlet fission.
• Distinguishing OS and CS components is crucial for predicting reactivity.