DNA Directed Organic Semiconductor Interactions Controlling Excitons, Charge Transfer States, and Singlet Fission

Excited states in organic semiconductors are generated, transported, and converted through π-orbital interactions between multiple molecules. Hence, efficiency depends on the relative geometries between molecules. Yet, control over spatial assembly of organic semiconductors is challenging. Large aromatic molecules will self-assemble into extended structures with no size or positional control. Deterministic interactions between two different semiconductor molecules is even rarer. In contrast, selective and high-yielding DNA base pairing interactions can control discrete, self-assembly of nanoscale structures. After introducing relevant synthetic and theoretical background to DNA assembly and interchromophore coupling, the synthesis of DNA-conjugated organic semiconductors are described. Semiconductors were inserted into the phosphodiester backbone of DNA, maintaining DNA’s self-assembling properties. The appended DNA direct the interactions between predefined numbers of the same molecule, followed by hetero-assemblies composed of different molecular backbones. DNA-directed changes are interrogated by excitonic couplings, using steady-state time-resolved optical spectroscopy to track the excited state evolution. Homo-aggregate molecules exhibit excitonic coupling. In contrast, heterostacks were capable of charge transfer between an electron-donor and electron-acceptor on DNA. Finally, singlet-fission active molecules were attached to DNA. This process generates two triplet excitons from one singlet exciton. The evolution of this process was tracked using time-resolved optical and magnetic spectroscopy. The combined observations in this thesis show multi-chromophore dependent phenomena are replicated in the aqueous DNA environment. Importantly, DNA successfully restricts and controls the extent of chromophore interaction to produce size-dependent phenomena and impart spatial control of multiple, different semiconductors