Molecules that absorb light through ligand-to-metal charge transfer (LMCT) and metal-to-metal charge transfer (MMCT)
To meet the energy demands for a sustainable future, abundant carbon-neutral sources of liquid fuel are needed. While existing technologies such as biomass conversion, wind electricity or photovoltaic cells can provide stopgap measures as carbon-neutral energy sources, large-scale liquid fuel production requires the development of new and direct solar-to-fuel technologies. Currently, there is no single device that efficiently incorporates the necessary elements for artificial photosynthesis into an integrated system.
Metal-to-metal charge transfer A d3-d0 Cr(III)-O-Ti(IV) complex
This project focuses on elucidating one of the requirements for solar fuel devices: the fundamental chemistry of excited state electron transfer from a chromophore to a fuel-producing reduction catalyst. In this area, a scientific gap is the control of excited state electron transfer out of the light absorbing chromophore. In order for excited state electron transfer to occur, the excited state must be sufficiently long-lived. Disovering new molecules is vital for fundamental studies of the properties important for efficient charge collection and utilization in solar-to-fuel systems. We are finding that dx-d0 (d3-d0 shown above) mono-oxido bridged heterobimetallic molecules can have visible-light induced metal-to-metal charge transfer (MMCT) transitions with lifetimes of over 100 ns. These types of molecules have potential advantages over existing systems in that properties such as excited state lifetimes and electron transfer rates can be tuned. They are also composed of abundant metals that are theoretically scalable for terawatt deployment. We also aretaking advantage of the properties of first row transiton metals (weaker bonds, low temperature spin-crossover, low spin-orbit coupling) in ways not previously done.
Application of BODIPY dyes as chromophores and fluorophores
BODIPY dyes are a robust platform for a variety of applications. We are studying how to utilize the synthetic versatility of BODIPY dyes in applications such as solar fuels (hydrogen generation), photodynamic therapy, upconversion and water-soluble fluorophores. We have demonstrated that optimizing intersystem crossing can be an efficient tool for enhancing the photocatalytic capabilities of this class of dyes for hydrogen and singlet oxygen generation. We have also developed methods for the synthesis of bright water-soluble BODIPY dyes that can be used as the central platform for biologically focused technologies such as imaging and sensing.
Functional carbon-based materials through the synthesis of extended arenes.
The synthesis of novel carbon-based electronic structures remains an important area of study for the next generation of nano-electronic applications. Historically, research on such structures has focused on conducting polymers, C60 derivatives, or carbon nanotubes. The research in our group explores the possibility for synthetically decorating cycloparaphenylene (cpp) “nanohoops” with metal-arene coordination compounds. These coordination complexes will then be used to link the cpp hoops together, and will serve as the building blocks for self-assembly of these molecular components into extended structures such as chains and nets. By taking a bottom-up approach to the synthesis of such structures, we gain the ability to finely tune the properties of the resulting materials. Of particular interest is controlling the rate and the mechanism of electron transfer through the resulting extended pi network by altering the oxidation state or coordination mode of the arene-metal complex.
We also are working on ways to use the resulting network as a template for the chemical growth of nanotube structures. The resulting material would reflect the structure of the initial self-assembly, and allow for single types of carbon nanotubes to be placed in pre-determined patterns.
Outside Collaborators include the Pushkar Group at Purdue University, the Tamblyn Group at the University of Ontario Institute of Technology, the Cuk Group at UC-Berkeley, and the Yachandra/Yano Group at LBNL.
Generous NCSU Startup Funds (Chemistry and College of Sciences)