Luminescence and Electron Dynamics in Atomically Precise Nanoclusters with Eight Superatomic Electrons

Abstract

The [Au25(SR)18]– and [Au13(dppe)5Cl2]3+ (dppe = 1,2-bis(diphenylphosphino)ethane) nanoclusters both possess a 13-atom icosahedral core with eight (8e) delocalized superatomic electrons, but their emission properties and time-resolved electron dynamics differ significantly. In this work, experimental photoluminescence and photoluminescence decay measurements are combined with time-dependent density functional theory calculations of radiative and non-radiative decay properties and lifetimes to elucidate the similarities and differences in the emission of these two nanoclusters with similar cores. In this work, the photodynamic properties of [Au13(dppe)5Cl2]3+ are elucidated theoretically for the first time. [Au13(dppe)5Cl2]3+ exhibits a single strong emission peak compared to the weaker bimodal luminescence of [Au25(SR)18]– (modeled here as [Au25(SH)18]–). The strongly emissive state is found to arise from deexcitation out of the S1 state, similar to [Au25(SH)18]–. Both theory and experiment exhibit microsecond lifetimes for this state. Transient absorption measurements and theoretical calculations demonstrate that the excited state lifetimes for higher excited states are typically less than 1 ps. The decay times for the higher excited states of [Au13(dppe)5Cl2]3+ and its model compound [Au13(pe)5Cl2]3+ (pe = 1,2-bis(phosphino)ethane) are observed to be shorter than the lifetimes of the corresponding states of [Au25(SR)18]–; this occurs because the energy gap separating degenerate sets of unoccupied orbitals is only ~0.2 eV in [Au13(dppe)5Cl2]3+ compared to a ~0.6 eV energy gap in [Au25(SH)18]–.