Ultrafast Dynamics of Complex Systems

Ultrafast spectroscopy • Nonlinear Microscopy • Computer Simulation • Nanoscale Materials • Devices • Inorganic Photophysics

With the advent of ultrafast laser technology has come the ability to follow the dynamics of chemical systems in “real time.” Here a chemical process is initiated via the absorption of a photon from laser pulse (termed the pump pulse) whose duration is short compared to the time scale of atomic or molecular motion. Evolution of the system is then followed in time with a second laser pulse (termed the probe pulse). Of particular interest are the time scales associated with the flow of energy and charge within complex molecular systems with the goal of understanding how the mechanisms and pathways of transport are connected with the structure of the material. Projects in our laboratory focus on complex chemical systems, including nanoscale materials, inorganic coordination complexes, and interfacial environments.

Research Directions

Nanomaterials:We are developing femtosecond pump-probe microscopy techniques for following the charge carrier (i.e. electron-hole) dynamics in photoexcited semiconductors with spatial resolution.  Current efforts target individual ZnO structures, as well as structures embedded field-effect transistor (FET) devices.

Molecular Materials:We are using a combination of ultrafast emission and computer simulation methods to follow the excited state energy and charge transport in functional molecular assemblies based on Ru(II) and Os(II) polypyridyl complexes that are bound to inert scaffolds (i.e. polymer or peptide) or incorporated in framework materials.

Molecular Excited States: Ultrafast pump-probe spectroscopies are being used to study the fundamental excited state energy- and electron-transfer, and more recently proton-coupled electron transfer (PCET) process that occur within molecular chromophores based on metal coordiantion complexes and small organic dyes.

Methods Development:The design and construction of spectroscopic instrumentation and computer models is an integral part of our research.  We have implemented femtosecond absorption, emission spectroscopies and polarization anisotropy methods.  Current projects are  developing ultrafast microscopy and non-linear Raman spectroscopies.

Funding:  Support for our current research is from the U.S. Department of Energy, UNC Energy Frontier Research Center (UNC-EFRC) on Solar Fuels and Next Generation Photovoltaics, the Army Research Office (ARO)  and the National Science Foundation (NSF). Past research projects have also received support from the National Aeronautics and Space Administration (NASA), Research Corporation and the ACS Petroleum Research Fund (ACS-PRF).

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