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Kenneth Knappenberger1 Hongjun Zheng1 Patrick Herbert1

1, The Pennsylvania State University, University Park, Pennsylvania, United States

Monolayer-protected clusters (MPCs) represent a class of nanomaterials that can be synthesized and isolated with structural (both compositional and geometric) specificity. Hence, MPCs provide model systems for understanding the nanoscale structure-function interplay. We have recently shown that femtosecond time-resolved two-dimensional electronic spectroscopy (2DES) can be used to isolate carrier dynamics of specific MPC electronic states.Here, 2DES studies of a family of MPCs in the 1-2 nm size range will be presented. These results show that the optical, electronic, and spin-state properties of MPCs are extremely sensitive to the electronic configuration of nanometal orbitals. For example, the magnetic properties of Au25(SR)18, where SR represents an alkanethiol, can be switched reversibly by oxidative opening of the eight-electron Superatom P orbital. Electronic interactions between assembled MPCs also exhibit spin-dependent magnetic phenomena not present in the isolated building blocks. Ultrafast spectroscopy on dimerized 20-atom MPCs reveal inter-particle spin-dependent dynamics not observed for the monomer. In contrast to the discrete carrier dynamics typical for MPCs, larger nanoparticles exhibit collective electronic behavior. I will provide a comprehensive description of how 2DES can be employed to describe the dynamics of metals spanning the non-metallic cluster and metallic particle domains.

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