Uncovering Nonadiabatic Dynamics of Plasmonic Metal–Molecular Switch Hybrids with Surface Hopping

Abstract Despite considerable interest in plasmonic nanoparticles for light-driven green chemistry under mild conditions, the mechanisms underlying their catalytic activity remain controversial. To resolve these mechanistic uncertainties, surface hopping has recently emerged as a powerful computational approach for atomistic descriptions of charge and energy flow at metal–molecule interfaces. Thus far, however, the method has been applied primarily to systems involving relatively small molecules such as H2 and CO, owing to the high computational cost of quantum-chemical calculations for metallic nanostructures. In the present work, we use surface hopping simulations to explore the nonadiabatic dynamics of an azobenzene molecule covalently bound to a gold nanocluster following either molecular or plasmon excitation. In accord with recent experimental observations, we find that the optically excited molecule gets rapidly quenched by the metal continuum via competing energy and charge transfer decay channels at short azobenzene–gold distances. On the other hand, the plasmon-excited gold nanocluster is nearly unaffected by the photoswitch and primarily relaxes via electron–phonon interactions due to an efficient electronic decoupling of the metal- and molecule-centered orbitals at the interface. In summary, our results provide direct atomistic insight into how undesired metal–molecule couplings can suppress the reactivity of functional molecules at plasmonic gold nanostructures, thereby facilitating the rational design of novel plasmonic systems.