University of Jyväskylä

Dissertation: 8.1.2016 FM Jaakko Koivisto (Faculty of Mathematics and Science, Physical Chemistry)

Start date: Jan 08, 2016 12:00 PM

End date: Jan 08, 2016 03:00 PM

Location: Ylistönrinne, KEM4

M.Sc. Jaakko Koivisto defends his doctoral dissertation in Physical Chemistry ”Electronic and Vibrational Spectroscopic Studies of Gold Nanoclusters”. Opponent Professor Thomas Bürgi (University of Geneva, Switzerland) and custos Professor Mika Pettersson (University of Jyväskylä). The doctoral dissertation is held in English.

Jaakko KoivistoM.Sc. Jaakko Koivisto defends his doctoral dissertation in Physical Chemistry ”Electronic and Vibrational Spectroscopic Studies of Gold Nanoclusters”. Opponent Professor Thomas Bürgi (University of Geneva, Switzerland) and custos Professor Mika Pettersson (University of Jyväskylä). The doctoral dissertation is held in English.

This thesis describes electronic and vibrational spectroscopic studies of monodisperse gold nanoclusters Au144(PET)60, Au68(mMBA)32, Au102(pMBA)44, and gold/silver alloys (Au/Ag)144(PET)60. The first electronic transitions, i.e. the optical gap, of the Au144(PET)60 and the (Au/Ag)144(PET)60 clusters were measured using absorption spectroscopy in the near infra-red (NIR). For pure gold cluster gap of 0.27 eV was measured, and for the silver-alloy clusters the gap was measured to be between 0.26 eV and 0.12 eV. Packing of the Au144(PET)60 molecules in single crystals were studied using IR-microscopy. Large inhomogeneous broadening of the IR-absorbance features of the PET-ligands was observed, indicating the ligands do not form ordered long-range structures in the crystals. The structure of Au68(mMBA)32 was determined using a combination of NIR-spectroscopy, electron microscopy, and computational calculations. The structure was found to be significantly less organized than expected for a small gold nanocluster, which is evident also from the small optical gap (0.31 eV) of the cluster. In last study the protonation of the para-mercaptobenzoic acid molecules used to protect the Au102(pMBA)44 nanocluster were studied using a combination of titration experiments and molecular dynamics simulations. A pKa of 6.18 was measured for the pMBAs attached to the cluster (free pMBA pKa = 4.16).  The MD simulations revealed a non-uniform surface charge distribution arising from the protonation states of the ligands at pH 6.20.

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Jaakko Koivisto
jaakko.m.koivisto@jyu.fi
+358408054505
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