posted on 2013-12-04, 00:00authored byChongyue Yi, Marcus A. Tofanelli, Christopher
J. Ackerson, Kenneth L. Knappenberger
Electronic energy relaxation of Au144(SR)60q ligand-protected nanoclusters,
where SR = SC6H13 and q = −1,
0, +1, and +2,
was examined using femtosecond time-resolved transient absorption
spectroscopy. The observed differential transient spectra contained
three distinct components: (1) transient bleaches at 525 and 600 nm,
(2) broad visible excited-state absorption (ESA), and (3) stimulated
emission (SE) at 670 nm. The bleach recovery kinetics depended upon
the excitation pulse energy and were thus attributed to electron–phonon
coupling typical of metallic nanostructures. The prominent bleach
at 525 nm was assigned to a core-localized plasmon resonance (CLPR).
ESA decay kinetics were oxidation-state dependent and could be described
using a metal-sphere charging model. The dynamics, emission energy,
and intensity of the SE peak exhibited dielectric-dependent responses
indicative of Superatom charge transfer states. On the basis of these
data, the Au144(SR)60 system is the smallest-known
nanocluster to exhibit quantifiable electron dynamics and optical
properties characteristic of metals.