Applications of conjugated polymers in photovoltaics and displays drive the need to understand how morphology and aggregation affect emission yields, spectra, and the facility with which charges are generated and migrate through the sample. It is known that solvent-polymer interactions in solution critically affect the properties of thin films formed when these solutions are evaporated onto substrates. Our work demonstrates that the propensity of conjugated oligomers and polymers to form emissive versus non-emissive aggregates in solution and in thin films is likewise governed by the solvent properties. Fluorescence correlation spectroscopy is used as a tool to identify both emissive and non-emissive species in dilute solutions while dynamic light scattering (DLS) is used to measure diffusion properties. In some solvents, such as toluene, conjugated materials form non-emissive aggregates even at picomolar concentrations. Under similar conditions, the same materials exhibit single-emitter properties in more polar solvents such as tetrahydrofuran (THF). These distinctions persist when the molecules are forcibly aggregated by addition of poor solvent and are correlated to variations in chain packing within the aggregate due to differences in their preferred conformation. Transient absorption spectroscopy is used to understand the impact of altering chain packing on the propensity for energy transfer and charge separation in the aggregated state and in films.
Linda A. Peteanu, Eric C. Wu, and Matthew Y. Sfeir, "Mechanisms underlying emission quenching in conjugated polymers: the role of inter-chain interactions (Conference Presentation)," Proc. SPIE 10348, Physical Chemistry of Semiconductor Materials and Interfaces XVI, 103480G (Presented at SPIE Nanoscience + Engineering: August 08, 2017; Published: 29 September 2017); https://doi.org/10.1117/12.2272793.5593147498001.
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