(6dj) Multi-Scale Modeling of the Structure and Dynamics of Bio-Inspired Light-Harvesting Technologies

Natural photosynthetic systems have engineered the ability to efficiently absorb and transport energy over long distances to the reaction center, where charge separation occurs. These energy transport properties are efficient due to the precise placement of optically-active chromophores, both weakly- and strongly-coupled, scaffolded in place by protein sub-units. When designing synthetic mimics of natural photosynthetic systems, an alternative to protein scaffolding is DNA nanotechnology, which has been used to scaffold chromophores by covalent and non-covalent interactions. Common closely-packed structural motifs seen in natural photosynthetic systems are strongly interacting J-aggregates, which extend the exciton delocalization length and increase the energy transport rate, and H-aggregated dimers, which increase the radiative lifetime of the exciton and can lead to charge separation. I have studied both FRET-based energy transport in DNA-intercalated thiazole orange dyes, and exciton delocalization in J-aggregated pseudoisocyanine fibers which self-assemble. These photosynthetic and DNA-templated systems require a multi-scale approach to modeling, so that dynamic motion of the complex can be captured (all-atom molecular dynamics), and so that the electronic structure of the excited states and excitons can be probed.

I am interested in studying the structural and electronic basis for the emergent photophysical behavior found in natural photosynthesis, and in applying these design principles to synthetic constructs. Long-range, or incoherent energy transfer between chromophores is well-studied, and can be adequately described by a Coulombic interaction between donor and acceptor transition charge densities, also known as FRET. Short-range energy transfer, on the other hand, is described by both Coulombic interactions as well as the electronic wavefunction overlap between the donor and acceptor chromophores. Short-range interactions lead to electronic properties such as exciton delocalization and charge separation. These short-range interactions are difficult to characterize, but are necessary for an adequate understanding of energy transfer properties in natural and synthetic constructs. In my future work, I will study the electronic structure properties of closely-packed chromophore systems, both in natural and synthetic complexes, to better understand how to build an energy capture device that can compete with the efficiencies seen in nature. Whether the properties of natural and synthetic light-harvesting complexes will converge or diverge will be of intense interest.

Postdoctoral Project: “Structure and function of DNA-templated chromophoric materials.” Under the supervision of Dr. Mark Bathe at Massachusetts Institute of Technology, in the Biological Engineering Department.

Ph.D. Dissertation: “A computational study of excitation energy transfer in photosynthetic light-harvesting complexes.” Under the supervision of Dr. Cynthia Lo at Washington University in St. Louis, in the Energy, Environmental, and Chemical Engineering Department.

Teaching Interests:

I have experience in teaching and mentoring over my entire scientific career, starting as a TA for Organic Chemistry laboratory while an undergrad at Bucknell University and several Chemical Engineering courses as a graduate student at Washington University, to teaching the undergraduate course entitled Modeling and Computing in Chemical Engineering after my graduate tenure as the instructor of record at Washington University. My teaching interests are interdisciplinary, as is my research, at the boundary between chemistry, biology, physics, and engineering, and I would feel comfortable teaching core Chemical Engineering courses as well as topics in multi-scale modeling and quantum chemistry.

Selected Publications:

WP Bricker & CS Lo. Excitation energy transfer in the peridinin-chlorophyll a-protein complex modeled using configuration interaction. Journal of Physical Chemistry B 118, 9141-9154 (2014).

WP Bricker & CS Lo. Efficient pathways of excitation energy transfer from delocalized S₂ excitons in the peridinin-chlorophyll a-protein complex. Journal of Physical Chemistry B 119, 5755-5764 (2015).

J Chmeliov, WP Bricker, C Lo, E Jouin, L Valkunas, AV Ruban & CDP Duffy. An ‘all pigment’ model of excitation quenching in LHCII. Physical Chemistry Chemical Physics 17, 15857-15867 (2015).

WP Bricker, PM Shenai, A Ghosh, Z Liu, MGM Enrinquez, PH Lambrev, H-S Tan, CS Lo, S Tretiak, S Fernandez-Alberti & Y Zhao. Non-radiative relaxation of photoexcited chlorophylls: Theoretical and experimental study. Scientific Reports 5, 13625 (2015).

K Pan, WP Bricker, S Ratanalert & M Bathe. Structure and conformational dynamics of scaffolded DNA origami nanoparticles. Nucleic Acids Research 45, 6284-6298 (2017).

PD Cunningham, WP Bricker, SA Díaz, IL Medintz, M Bathe & JS Melinger. Optical determination of the electronic coupling and intercalation geometry of Thiazole Orange homodimer in DNA. Journal of Chemical Physics 147, 055101 (2017).

WP Bricker, JL Banal, MB Stone & M Bathe. Molecular model of J-aggregated pseudoisocyanine fibers. Journal of Chemical Physics 149, (2018). In Press.