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Research

1. Ultrafast Interfacial Charge Transfer Dynamics in Dye-Sensitized TiO₂ nanoparticles

The everlasting thrust for cost-effective alternative energy resources is one of the main interests of the group. The research efforts are focused on investigating the dynamics of interfacial charge transfer in donor-p-acceptor chromophore sensitized TiO₂ nanoparticles. The idea is to probe the local electric fields in dye-sensitized TiO₂ nanoparticles using ultrafast transient absorption spectroscopy and femtosecond fluorescence upconversion. The idea is to use these local electric fields to amplify the nonlinear optical properties of chromophores. (Collaborators- Synthesis of chromophores: Ekkehard Sinn (WMU), Giribabu, L.; Rao, V. J. (IICT, India), Theory- L.G.C. Rego (Brazil))

2. Highly Efficient Two-photon Materials – Hybrid Chromophore/Semiconductor and Chromophore/Metal Nanocomposites

Two-photon optical materials with enhanced cross-sections are pursued in my research group especially in the context of their applications in multi-photon imaging and optical limiting. The idea is to apply the principles present in the field of dye-sensitized solar cells towards making better two-photon materials. Here, the focus is on the dye molecules functionalized semiconductor nanoparticles and dye functionalized metal clusters. Main idea of my research group is to use the local electric fields that are prevalent at the interfaces to enhance the TPA cross-sections of stationed chromophores. (Collaborator: Prof Ekk Sinn)

3. Ultrafast and Temperature-Dependent Optical Properties of Quantum-sized Metal and Semiconductor Nanoclusters

          Time-resolved luminescence of quantum-sized gold clusters and semiconductor nanomaterials are being investigated with femtosecond fluorescence upconversion measurements. Also, temperature-dependent optical properties of atomically precise metal clusters are studied to understand the role of core to shell transitions and exciton-phonon interactions. The studies provide unique aspects during the evolution of molecule to metal and molecule to semiconductor energy levels. Interesting fluorescence from quantum-sized gold clusters is observed which showed larger hot excited state lifetimes. (Collaborator: Prof. Rongchao Jin (Carnegie Mellon))

4. Biophysics via Two-photon Absorption Cross-section and Ultrafast Fluorescence Spectroscopy

Novel nonlinear optical and ultrafast spectroscopic techniques are being employed to study protein folding and unfolding, metal bonding to proteins. The idea is to probe the local electric fields with optical spectroscopic techniques to monitor the biophysical processes. In aiddtion, intrinsic fluorescence of tyrosine is probed with femtosecond fluorescence upconversion to understand the structural aspects of protein folding in the Wilson’s disease protein (Collaboration with Prof David Huffman, WMU). Femtosecond fluorescence anisotropy measurements are being utilized to understand the auto fluorescence resonance energy transfer in fluorophore-labeled proteins.

5. Turn-on Luminescent Sensors for Dissolved Oxygen and Metal Ions

Surface states of ZnO nanoparticles are being modified to achieve materials that can work as tunr-on luminescent dissolved oxygen sensors. The applications of these sensors include aviation pressure sensors and oil spill leak. Also, nonlinear optical sensors with turn-off and turn-on two-photon excited fluorescence are being investigated. The main idea is to achieve stand-off detection with multi-photon sensing. Organic dye molecule based sensors are also being investigated in the lab for metal ions, energetic materials and chemical warfare agents. Mechanistic aspects of the sensing are probed with time-resolved spectroscopic techniques.

Collaborators

Prof David Huffman – Department of Chemistry, WMU

Prof Ekkehard Sinn – Department of Chemistry, WMU

Prof Sherine Obare – Department of Chemistry, WMU

Prof Clement Burns- Department of Physics, WMU

Prof Dongil Lee - Yonsei University – S Korea

Prof Ronchao Jin - Carnegiel Mellon University - Pittsburgh

Dr Lingamallu Giribabu, Indian Institute of Chemical Technology, Hyderabad INDIA

Dr V. Jayatirtha Rao, Indian Institute of Chemical Technology, Hyderabad INDIA

Prof Valery Bliznyuk, WMU

Prof Muralidhar Ghantasala – Mechanical and Aeronautical Engg, WMU

Prof Tianshu Liu - Mechanical and Aeronautical Engg, WMU

Prof Gellert Mezei – Department of Chemistry, WMU

Prof Theodore Goodson III - University of Michigan,  Ann Arbor

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