Ultrafast Dynamics of Competing Dimethyl Disulfide Photodissociation Pathways

Disulfide photochemistry impacts a wide range of chemical processes from biological UV photodamage to polymer self-healing and green photocatalysis. Despite this, the response of disulfide bonds to deep-UV light remains poorly understood. Dimethyl disulfide serves as a model system for understanding the fundamental properties of this chemical motif, including its UV photodynamics. While 267-nm excitation exclusively cleaves the S–S bond on a subpicosecond time scale, 200 nm excites electronic states of Rydberg and antibonding character, resulting in competing C–S and S–S dissociation on an unknown time scale. Using mega-electron-volt ultrafast electron diffraction and time-resolved velocity-mapped ion imaging, we find subpicosecond as well as unexpectedly long, picosecond lifetimes. Nonadiabatic mixed quantum-classical dynamics reveal mechanisms and observables. We attribute the subpicosecond dynamics to bond dissociation on singlet states and the picosecond dynamics to dissociation after intersystem crossing. Our study reveals that deep-UV excitation in disulfide-containing molecules can induce complex, multi-time scale dynamics.