Understanding Coherent and Spin-Polarized Dynamics in Metal Nanoclusters

The influence of atomic- and molecular-level structure on chiroptical excitation, spin, and electron dynamics in monolayer-protected clusters (MPCs) will be described. Gold nanoclusters spanning from sub-to-two nanometer –diameters show a diverse range of magneto-chiral excitation behaviors. The visible magnetic circular dichroism (MCD) spectrum of Au₁₄₄(SC₈H₉)₆₀ includes nineteen distinct peaks. Among these, signatures of paramagnetic, diamagnetic, and mixed charge transfer excitations are all resolved. The results indicate that structurally well-defined gold clusters near the onset of metallicity present many opportunities for understanding and tailoring spin properties at metal-ligand interfaces. Of particular interest, the influence of metal-ligand vibrations on the persistence of spin-polarized excitation has been examined. Signatures of strong vibronic coupling between metal electrons and ligand vibrations were detected for paramagnetic excitation in gold MPCs. Using ultrafast multi-dimensional spectroscopy, the influence of vibrational coupling on coherence lifetimes was resolved with both state and mode specificity. The results demonstrate the capability of advanced spectroscopic methods for determining structure-property correlations in metal nanoparticles.