Optical Properties and Electronic Energy Relaxation of Metallic Au_(144)(SR)_(60) Nanoclusters

摘要

Electronic energy relaxation of Au_(1440(SR)_((60)~q) ligand-protected nanoclusters, where SR = SC_6H_(13) 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 Au_(144)(SR)_(60) system is the smallest-known nanocluster to exhibit quantifiable electron dynamics and optical properties characteristic of metals.