Electronic energy relaxation of Au144(SR)60q monolayer-protected nanoclusters, SR = SC6H13 and q = -1, 0, +1, and +2, was examined using femtosecond time-resolved spectroscopy. Au144(SR)60 nanoclusters were excited by 400-nm light and probed using continuum pluses. Global regression analysis of the transient data revealed multiple components: 1) transient bleaches at 525 nm and 600nm, 2) broad visible excited-state absorption (ESA), and 3) stimulated emission (SE) at 670 nm. The transient bleach exhibited excitation power-dependent relaxation, which is a hallmark of electron-phonon coupling in metals. The prominent 525-nm bleach was assigned to a core-localized plasmon resonance. Oxidation-state dependent kinetics of ESA resulted from metal-sphere charging process. The dynamics, emission energy, and intensity of the SE peak exhibited dielectric-dependent responses indicative of metal-nanocluster-to-ligand charge transfer. These results indicated Au144 nanocluster exhibit both metallic and molecular-like properties. To our knowledge, Au144 is the smallest nanocluster known to exhibit both molecular and metallic behavior.

Optical properties and electronic energy relaxation of monolayer-protected nanoclusters

247th National Meeting (2014)

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