Triplets in the cradle: ultrafast dynamics in a cyclic disulfide

Area of Science:

• Photochemistry
• Theoretical Chemistry
• Chemical Physics

Background:

• Ultrafast dynamics of cyclic disulfides are crucial for understanding photochemical pathways.
• Spin-orbit coupling plays a significant role in nonadiabatic processes.
• 1,2-dithiane serves as a model system for studying disulfide photochemistry.

Purpose of the Study:

• To investigate the theoretical effect of spin-orbit coupling on "Newton's cradle"-type photodynamics in 1,2-dithiane.
• To elucidate the influence of triplet states on singlet state population dynamics and radical recombination.

Main Methods:

• Simulations of ultrafast nonadiabatic dynamics using surface-hopping trajectories.
• Ab initio electronic structure calculations at the SA(4|4)-CASSCF(6,4) level.
• Comparison of simulations including only singlet states versus those including both singlet and triplet states.

Main Results:

• Triplet states were found to deplete the singlet state population in 1,2-dithiane.
• Long-time populations of singlet and triplet states approached their statistical limits.
• Intersystem crossing between singlet and triplet manifolds was identified as a key process.

Conclusions:

• Spin-orbit coupling significantly alters the photodynamics of 1,2-dithiane by involving triplet states.
• Triplet states effectively hinder intramolecular thiyl radical recombination.
• Understanding these dynamics is crucial for controlling photochemical reactions involving disulfides.