Research
The Powers-Riggs Lab is interested in understanding how molecules absorb light, and how their environment promotes or prevents this process. By better understanding light absorption, scientists can design more effective solar-driven processes, from solar panels to catalysts for renewable fuels.
Porphyrin, the centerpiece of our research, is a pyrrole-based macrocycle. It has a similar structure as chlorophyll, making it an excellent light absorber, and hemoglobin, making it capable of binding to a variety of ligands. These factors make porphyrins an excellent model to explore geometric considerations of Donor-Acceptor interactions.
Research in the Powers-Riggs group has focused on identifying promising binding motifs for zinc-based porphyrin (ZnTPP). Nitrogen containing moieties are known to coordinate with the zinc center, thus laying the groundwork for more complicated structures.
Axially-Coordinated Donor-Acceptor Complexes
Metal-porphyrins exhibit the ability to form a variety of complex geometries through non-covalent coordination of the metal center. Here, we bind use zinc tetraphenylporphyrin to coordinate with pyridine- and imidazole- containing compounds.
By attaching an electron-accepting molecule to the amide linker, we can create electron transfer complexes that can be studied through steady-state spectroscopy, such as UV-visible absorption or fluorescence, as well as time-resolved methods.
Non-Covalent Assemblies
When two identical chromophores lie in close proximity, orbital overlap and coupling leads to distinct changes to the ground and excited state energy levels. Historically, Kasha’s model of exciton coupling dominated understanding of molecular aggregates by reducing molecular dimers to their respective dipoles, and, depending on the angle and distance between the two, has clear predictable effects on the absorption and emission properties. Recently, Spano and coworkers have expanded on this model to include short-range charge transfer coupling in order to explain a larger class of aggregate behavior. Geometric alignment is important for understanding the photophysics of aggregates as well, and self-assembly techniques provide a clear path toward tuning the electronic properties of such clusters.