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DNA Directed Organic Semiconductor Interactions Controlling Excitons, Charge Transfer States, and Singlet Fission 10.17863/CAM.60564 Gorman, Jeffrey 0000000268887838 Friend, Richard 0000000165656308 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. University of Cambridge 2020-09-15 Thesis Doctoral Doctor of Philosophy (PhD) eng https://www.repository.cam.ac.uk/handle/1810/313457 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/89ab79da-cbba-4112-a9a0-b78423c04231/download c269a4b83973df7b7d0ca44835465b4b https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/0c03bbf1-a51d-486b-a6f5-fac0f3947d41/download 353adac0d1ebdfd65ab16480263c3c87 https://www.rioxx.net/licenses/all-rights-reserved/ DNA Singlet Fission Organic Semiconductor Charge Separation Excitonic Coupling Self Assembly