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| Searle Chemical Laboratory 023 |
| Searle Chemical Laboratory 030 |
| 773-834-1877 |
| 773-702-0805 |
| spark8@uchicago.edu |
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| (Anticipated) PhD in Chemistry, University of Chicago, Chicago, IL |
| M.S. Chemistry, Korea University, Seoul, Korea |
| B.S. in Chemistry, Korea University, Seoul, Korea |
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| I. Solvent dynamics in chemical systems |
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| Solvation is a relaxation of solute-solvent systems after a sudden perturbation of electronic structure in the solute. The relaxation takes place by solvent molecular reorganization. Therefore, solvation has to be understood in terms of solvent molecular responses. Solvation has been extensively studied by fluorescence Stokes shift (FSS) and photon echo (PE) measurements. In these methods, the solute is used as a probe and time-dependent change in solute properties (emission spectra in FSS and transition frequency in PE) are measured. Therefore, the information from those measurements is limited. However, direct measurement of the solvent is quite challenging. We have developed spectroscopic methods to measure the solvent responses in non-reactive and reactive systems. |
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| 1) Two-color OKE spectroscopy is performed in an OKE configuration as a resonant-pump nonresonant probe polarization method. Two-color OKE (TC-OKE) method is a variant optical Kerr effect (OKE) spectroscopy which has been used to study pure liquid dynamics. In the TC-OKE method, resonant-pump excites the solute and as a consequence the solvent reorganization is induced. The time-delayed nonresonant probe selectively measures the anisotropic solvent responses during the solvation. The TC-OKE method allows measuring the solvent spectral density in solvation. It is also applicable to other reactive systems in liquids (e.g. photodissociation, charge transfer, and so forth) |
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| 2) Resonant-pump polarizability response spectroscopy (RP-PORS) is a comprehensive spectroscopic method for measuring the iso- and anisotropic solvent responses in solvation. Basically, it is an optical heterodyne detected transient grating (OHD-TG) spectroscopy with a resonant pump added. The OHD method allows selective measurements of the real and imaginary parts of the third-order polarization. By polarization-sensitive measurements, the iso- and anisotropic tensor elements are obtained. It can be extended to a two-dimensional (2D) PORS spectroscopy by giving a time delay between the resonant and nonresonant pumps. 2D-PORS is used to measure the instantaneous solvent spectral density along the solvation axis showing how the solvent spectral density evolves in solvation. |
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| II. Electron dynamics in Au nanorods |
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| Electrons in the Fermi level are described as electron gas that can freely move in metal. When electrons are confined in nanoscale particles, they show a collective behavior called surface plasmon oscillation that doesn’t exist in bulk. In Au nanorods, there are two surface plasmon modes : longitudinal and transverse modes that are parallel and perpendicular along the long axis of the nanorod, respectively. By changing the aspect ratio, the resonant frequency of the longitudinal mode can be varied. The longitudinal mode of surface plasmon is selectively excited without inducing interband transition. Ultrafast surface plasmon and related electron dynamics can be studied. Four-wave-mixing spectroscopy is used to measure changes in the real (dispersive) and imaginary (absorptive) parts of the complex refractive index associated with electron-electron scattering and electron-phonon relaxation in Au nanorods. |
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