Monolayer-protected metal nanoclusters (MPCs) including [Au25(SR)18], [Au38(SR)24], Au102(pMBA)44], [Au144(pMBA)60], and [Au144(SR)60], (SR = S(CH2)2Ph; pMBA = p-mercaptobenzoic acid) were examined using magneto-optical and femtosecond time-resolved spectroscopies. Superatom models described Au25 and Au38 MPC dynamics Spectrally resolved femtosecond time-domain measurements revealed an energetic barrier and oxidation-state dependence for electronic relaxation rate constants. Time-resolved magneto-optical measurements confirmed intersystem crossing relaxation and microsecond radiative decay of high-spin states, suggesting key roles for Superatom unpaired electrons. Conversely, Au144 MPC differential transient spectra contained transient bleaches, excited-state absorption (ESA), and stimulated emission (SE). Excitation pulse-dependent bleach recovery reflected electron-phonon coupling, with a core-localized plasmon resonance yielding the 525-nm bleach. Oxidation state-dependent ESA decay kinetics required a metal-sphere charging model. SE peaks exhibited dielectric-dependent responses, indicating metal nanocluster-core-to-ligand charge transfer. Au144(SR)60 MPCs represent the smallest-known nanocluster exhibiting metalic electron dynamics. Structure-dependent nanocluster photo-induced dynamics and optical properties evolved from molecular to bulk-like between Au25 and Au144.

Superatom photochemistry and the search for the incipient plasmon

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.