Chasing Excited States: Dynamics at the Edge of Chemical Reactivity

Transition-metal complexes exhibit rich photochemical and photophysical properties due to their ability to access long-lived electronically excited states. Replicating such behavior in first-row (3d) transition metals presents significant challenges and requires detailed insight into excited-state dynamics. In this work, I present excited-state dynamical simulations using mixed quantum-classical non-adiabatic surface-hopping and quantum multi-layer MCTDH methods to unravel the excited-state dynamics of cobalt(III) photosensitizers. Initial triplet population timescales are obtained from simulated population dynamics, while long-time recovery is additionally described using transition state theory. The simulations show that ultrafast relaxation emerges from the interplay of spin–orbit coupling, vibrational coherence, and structural dynamics. Overall, this work demonstrates that combining complementary simulation approaches is essential for understanding complex excited-state processes.