Organic semiconducting chromophores have been used for a wide variety of electronic, optoelectronic, and biological applications. They offer solutions to global problems including the need for renewable energy and new and improved medical therapeutics and diagnostics. In optoelectronics, organic semiconductors can function as light harvesting materials in traditional photovoltaics (PVs) and transparent photovoltaics (TPVs). TPVs utilize organic semiconductors to absorb near-infrared and ultra-violet light, allowing visible light to pass through the device, and can be integrated with surfaces otherwise inaccessible for traditional PVs. In medical therapeutics and diagnostics, organic semiconducting chromophores function as active agents in light-based treatments such as photodynamic therapy, or as highly fluorescent imaging agents to aid in the detection of illnesses.The first portion of this thesis details three projects focused on PVs. To begin, four new organic salt semiconductors, comprised of an organic chromophore and a counterion, are demonstrated in PVs. Device data is analyzed with experimental and computational methods to reveal a strong correlation between the total charge character on the chromophore and the carrier mobility in bulk films. In the second project, high efficiency TPVs are fabricated with a selectively near infrared absorbing polymer and non-fullerene acceptor via layer-by-layer deposition. TPVs achieved a power conversion efficiency of 8.8%, average visible transmittance of 40.9%, and light utilization efficiency of 3.6%, among the highest reported. Using the layer-by-layer approach, the impact of the full range of polymer thickness on electronic and optical device performance is evaluated. The last PV project presents the first demonstration of graphene nanoribbons as an active material in PVs with a detailed analysis of underlying exciton diffusion and charge collection mechanisms.The second portion of this thesis demonstrates the translation of a series of fluorescent organic salts with various counterions developed as PV materials in the first half of the thesis into a platform for photodynamic therapy and fluorescent imaging. Organic salts are formulated into nanoparticles and found to selectively accumulate in tumor cells, where the counterion tunes the frontier energy levels and the toxicity of the salt. Organic chromophores paired with small, hard counterions are found to be cytotoxic while bulky and often halogenated counterions cause the salts to be nontoxic at high dosages, ideal agents for bioimaging. Between the two extremes are several organic salts that are selectively phototoxic and are excellent candidates for photodynamic therapy. Organic salt nanoparticles are characterized with a variety of spectroscopic techniques to understand the size and optical properties. Subsequently, organic salts are demonstrated as effective active agents for treating cancer via photodynamic therapy in a mouse model. Collectively, we demonstrate a vast range of processing, characterization, and applications for new organic semiconductors in two key fields that are united by their molecular chemistry.
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