Theoretical Design of Molecular Nanostructures for Exciton Control

Abstract

Organic semiconductors comprised of strongly-coupled chromophores harness control of delocalized excitations, or excitons, via programmed molecular structures. The dynamics of these excitons enable energy and information transfer within molecular networks, positioning chromophore assemblies as ideal candidates for a number of technologies such as solar energy conversion, nanoelectronics, and quantum computing. Despite significant advancements, there exists no universal model that can explain the dependence of exciton photophysics on molecular morphology. This thesis employs mathematical and atomistic models to contribute key physical insights into the interdependencies between chromophore spatial organization and exciton dynamics, shaped by inter-chromophore couplings and interactions with the thermal bath.

In the first part, a Frenkel Exciton-based model is introduced as a strategy for studying exciton evolution between precisely arranged chromophores. In Chapter 2, I develop a novel approach to map unitary quantum computing operations to Hamiltonians describing excitonic circuits in the presence of a model bath. Then, Chapter 3 scales this framework to complex quantum algorithms represented by explicit molecular systems. Finally, Chapter 4 presents an innovative molecular approach for directing exciton flow via geometrical phase in tightly-bound chromophore arrays.

The second part delves into the intricacies of exciton interaction in densely packed molecular systems arranged within DNA scaffolds. Chapter 5 combines molecular dynamics and quantum mechanical calculations, further validated by experimental results, to study the interplay between long-range electrostatic and short-range charge transfer interactions. Chapter 6 then correlates this interplay with geometrical configurations derived from the DNA scaffolding. This thesis culminates in Chapter 7, which introduces a computational pipeline designed to leverage the precise control over excitons afforded by macromolecular frameworks, paving the way for custom-tailored DNA-based excitonic circuits.