Femtosecond IR Probe of Ultrafast Dynamics of Molecular Adsorbates on Nanoparticles: Solvation and Electron Transfer

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Dr. Tianquan Lian of Emory University is funded for his research on femtosecond IR probe of ultrafast dynamics of molecular adsorbates on nanoparticles - solvation by a grant in the Physical Chemistry program of the Chemistry Division. He will further develop and test the theory of solvation-induced vibrational peak shift and use this novel approach to study solvation dynamics of molecules at nanoparticle/liquid interfaces. For molecules with large dipole moment changes between ground and excited states, femtosecond excitation prepares the excited molecule in a non-equilibrium solvent configuration. The effect of the subsequent solvation on solute vibrational spectra is not yet understood, unlike the well-studied effect on solute electronic spectra. He is developing a theory of solvation-induced solute dynamic vibrational peak shift based on the Onsager dielectric continuum model of solvent-solute interaction. Dynamic peak shifts will be measured in Re(dcbpy)(CO)3Cl and related molecules in different solvents. The magnitude and dynamics of the CO stretching peak shifts will be used to compare with and critically test the theoretical model. He also will use vibrational peak shift as a new method to study solvation dynamics at solid-liquid interfaces. The combination of IR probe and nanocrystalline films will allow the study of solvation dynamics in a wide range of solvents. This approach is complementary to existing techniques such as fluorescence Stokes shift and the optical Kerr effect, and may have unique applications in slightly scattering media such as nanocrystalline thin films, that are difficult to study using these extant techniques. The proposed research is a continuation of Dr. Lian's research effort in understanding ultrafast dynamics of molecular adsorbates on nanoparticles. Semiconductor and metal nanoparticles have many potential applications ranging from nanoelectronics, solar energy conversion, to biomedical-imaging. Most nanoparticles are synthesized or modified with attached molecules as passivating, structural linkage, sensitizing, or molecular sensing groups. These molecules play essential roles in transfer, transport and dissipation of charge and energy in these systems. The proposed work will lead to a fundamental understanding of the dynamics of molecules on the nanoparticle surface, such as solvation and energy relaxation. This knowledge is essential to developing more efficient devices based on nanoparticles. The proposed research will also allow the training of postdoctoral fellows, graduate students and undergraduate students in the area of nanoscience and nanotechnology, educating the workforce of the future.