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Ultrafast Relaxation Dynamics of Au (SCHPh) Nanoclusters and Effects of Structural Isomerism Meng Zhou, Shubo Tian, Chenjie Zeng, Matthew Y. Sfeir, Zhikun Wu, and Rongchao Jin J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b10360 • Publication Date (Web): 22 Dec 2016 Downloaded from http://pubs.acs.org on December 29, 2016
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The Journal of Physical Chemistry
Ultrafast Relaxation Dynamics of Au38(SC2H4Ph)24 Nanoclusters and Effects of Structural Isomerism Meng Zhou,1 Shubo Tian,2 Chenjie Zeng,1 Matthew Y. Sfeir,3 Zhikun Wu,2 Rongchao Jin1* 1
Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanotechnology, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, Anhui 230031, China. 3 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA 2
Abstract: Structural isomerism in nanoparticle 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 Au38(SC2H4Ph)24. The biicosahedral Au38 (denoted as Au38Q) with an Au23 inner core in its atomic structure shows rapid decay (1.5 ps) followed by nanosecond relaxation to the ground state, whereas its structural isomer (Au38T) exhibits similar relaxation processes but the rapid decay is accelerated by ~50% (1.0 ps). The fast 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 Au38T is ascribed to its unique core structure which is made up of a mono-icosahedral Au13 capped by an Au12 tri-tetrahedron by sharing two atoms. Interestingly, coherent phonon emissions (25 cm-1 for Au38Q, whereas 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 the same sized gold nanoclusters.
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The Journal of Physical Chemistry
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Introduction Structural isomerism refers to the phenomenon that molecules have the same atomic composition but different arrangements of atoms in space. Observation and understanding of isomerism for nanostructures remains a major challenge since it has long been difficult to obtain nanoparticles of the same formula and resolve their atomic structures. Thiolate-protected ultrasmall gold nanoparticles (often called nanoclusters, typically 1-3 nm) have emerged as a new class of materials that offer an ideal system to investigate the isomerism phenomenon at the nanoscale because it has been possible to precisely control gold nanoclusters at the atomic level by novel synthetic methods and some of the nanocluster structures have been solved by single-crystal X-ray diffraction.1-8 Investigation on the energy relaxation dynamics of the nanoclusters with different sizes and structures will allow one to understand their physical and chemical properties as well as to facilitate the development of applications.9-20 Femtosecond spectroscopy of plasmonic gold nanoparticles (typically >2 nm) shows that their electron-phonon and phonon-phonon interactions are strongly dependent on size.21-25 For ultrasmall gold nanoparticles (
