Ultrafast Relaxation Dynamics of Au38(SC2H4Ph)24 Nanoclusters and Effects of Structural Isomerism

Structural isomerism in nanoparticles has recently emerged as a new topic and stimulated research interest because the atomic structures of ultrasmall nanoparticles may have great impact on their fundamental properties and applications. Here we report the correlation between ultrafast relaxation dynamics and atomic structures of two isomers of thiolate-protected Au-38(SC2H4Ph)(24). The bi-icosahedral Au-38 (denoted as Au(38)Q) with a Au-23 inner core in its atomic structure shows rapid decay (1.5 ps) followed by nanosecond relaxation to the ground state, whereas its structural isomer (Au-38T) exhibits similar relaxation processes, but the rapid decay is accelerated by similar to 50% (1.0 ps). The picosecond relaxations in both cases can be assigned to core shell charge transfer or electronic rearrangement within the metal core. The acceleration of the fast decay in AU(38T) is ascribed to its unique core structure, which is made up of a mono-icosahedral Au-13 capped by a Au-12 trketrahedron by sharing two atoms. Interestingly, coherent phonon emissions (25 cm(-1) for AU(38)Q 27 and 60 cm (-1) for Au38T) are observed in both isomers with pumping in the NIR region. Our results illustrate for the first time the importance of atomic structures in the photophysics of same sized gold nanoclusters.