The formation and decay of the optical hole (bleach) for 4 nm CdSe nanoparticles (NPs) with adsorbed electron acceptors (1,4-benzoquinone and 1,2-naphthoquinone) and the rise and decay of the reduced electron acceptors formed after interfacial electron transfer from the CdSe NPs were investigated by femtosecond laser spectroscopy. The ultrashort (200-400 fs) rise times of the bleach at the band-gap energy of the CdSe NP as well as of the acceptor radical anion are found to increase with increasing the excitation energy. This suggests that the electron transfer from the CdSe NP to the quinone electron acceptor occurs after thermalization of the excited hot electrons. The decay times of the transient absorption for the electron acceptor radical anions are found to be comparable to that of the CdSe NP bleach recovery time (3 ps). This suggests that the surface quinones shuttle the electron from the conduction band to the valence band of the excited NP. We contrast this behavior with the excited-state dynamics of the recently investigated CdS-MV 2+ system in which the electron acceptor does not shuttle the accepted electron back to the hole in CdS.

Formation of metallic nanoparticles produces an increased surface area per unit volume of material, which provides potential applications in enhancing surface catalyzed reactions. Recently, attention has been focused on moving from the solution based syntheses to solid phase materials by arranging such particles into well ordered 2- and 3- dimensional structures, or forming cluster engineered materials that posses well defined structures. Such studies have shown the importance of size, size distribution, and shape of particles upon self assembled monolayers. We have recently prepared shape-controlled Pt nanoparticles with ﹛111﹜ (tetrahedral), ﹛100﹜ (cubic), and mixed ﹛111﹜ - ﹛100﹜ (truncated octahedral) faces. To study how these faces may orient to form particle point superlattice structures we have prepared monolayer distributions of Pt particles in humidity chambers for analysis by TEM.Our shape controlled Pt particle synthesis yields between 60 and 80 % cubes, tetrahedra, or truncated octahedra with average diameters ≥ 7 nm.