Triplets in the cradle: ultrafast dynamics in a cyclic disulfide

TL;DR

This study uses advanced quantum chemical simulations to explore how spin-orbit coupling influences ultrafast photodynamics in cyclic disulfide, revealing triplet states' role in population depletion and reaction pathway hindrance.

Contribution

It provides the first detailed theoretical analysis of triplet state effects on ultrafast dynamics in cyclic disulfides using surface-hopping simulations.

Findings

Triplet states deplete singlet populations over time.

Intersystem crossing hinders radical recombination pathways.

Presence of triplet states affects overall photodynamic behavior.

Abstract

The effect of spin-orbit coupling on the "Newton's cradle"-type photodynamics in the cyclic disulfide 1,2-dithiane (C4H8S2) is investigated theoretically. We consider excitation by a 290 nm laser pulse and simulate the subsequent ultrafast nonadiabatic dynamics by propagating surface-hopping trajectories using SA(4|4)-CASSCF(6,4)-level electronic structure calculations with a modified ANO-R1 basis set. Two simulations are run: one with singlet states only, and one with both singlet and triplet states. All trajectories are propagated for 1 ps with a 0.5 fs timestep. Comparison of the simulations suggests that the presence of triplet states depletes the singlet state population, with the net singlet and triplet populations at long times tending towards their statistical limit. Crucially, the triplet states also hinder the intramolecular thiyl radical recombination pathway via the efficient intersystem crossing between the singlet and triplet state manifolds.