About the Seminar:

Title:

An exciton in a complex world: Environment-controlled photophysics in light harvesting

Abstract:

Excitons are the molecular scale currency of electronic energy. Control over excitons and their dynamics enables energy to be directed and harnessed for light harvesting and molecular electronics, yet these dynamics strongly depend on the surrounding environment. Describing – and controlling – this dependence is challenging in condensed phase systems owing to the large number of degrees of freedom. We disentangled the effects of the environment for two systems. First, we performed ultrabroadband 2D electronic spectroscopy on the primary antenna protein from green plants, LHCII. We found that the two chemically identical carotenoids in LHCII serve distinct roles owing to their individual protein binding pockets. On one carotenoid, we discovered a debated dark state that mediates exciton relaxation from higher lying electronic states to serve as a nexus of light harvesting [Son, et al., Chem, 2019]. On the other, we directly measured exciton transfer into its short-lived S 1 state, a hypothesized but previously unobserved pathway to safely dissipate excess excitons, to regulate light harvesting [Son, et al., Nat Communs, 2020]. Second, we developed a synthetic system consisting of chromophores held in a DNA scaffold. In a cy3-DNA assembly, we increased the efficiency of exciton transfer by 30%
through the introduction of a fluctuating scaffold [Hart, et al., Chem, 2021]. In a squaraine-DNA assembly, we used the scaffold to precisely position the chromophores for symmetry-breaking charge transfer, which had not been previously achieved in these molecules despite decades of study [Hart et al., Chem Sci, 2022]. Collectively, these two systems provide an experimental demonstration of how the environment can direct exciton dynamics.

About the Speaker:

Research:

Research in our group is inherently multidisciplinary; we combine tools from chemistry, optics, biology, and microscopy to develop new approaches to probe dynamics. We study dynamics in two classes of systems: biological and bio-inspired light-harvesting systems that are of interest to solar energy research and biomass production; and bacterial and mammalian receptor proteins that are targets for human therapeutics. To explore these systems, we use ultrafast transient absorption spectroscopy, single-molecule fluorescence spectroscopy, and develop model membrane systems.