Although tremendous advances have been made in semiconducting polymer-based devices, in many cases, the specific molecular conformations that enhance device efficiency are not known. In this project, we explore methods to control polymer conformation and donor-acceptor local packing in semiconducting polymer assemblies to identify molecular geometries that can facilitate excited state electron transfer, and discourage back electron transfer. To achieve this, we design amphiphilic semiconducting polymers based on combinations of thiophene, fluorine and cyclopentadithiophene units with charged alkyl side chains. This allows polymers to assemble into cylindrical micelles in water with the polymer chains running along the micelle long axis. Solution small-angle X-ray scattering (SAX) data proved that these polymers form nearly straight micelles. We then assembled excited state electron acceptors such as perylene diimide (PDI) or fullerene derivatives with the polymer micelles. Depending on their sizes and mixing condition, the position of the acceptors can be either in the polymer micelles or outside the micelles. Photoluminescence quenching of the polymer by these acceptors indicates excited-state charge transfer which generally results from physical contact between donors and acceptors. We find that THF annealing increased quenching, indicating that more acceptors are driven into the micelles. PDI based acceptors can quench polymer luminescence more efficiently than fullerene based acceptors, indicating that the smaller size of the PDI acceptors influences the amount of acceptors that can incorporate into the micelles. Generally we find that acceptor size and solution mixing conditions can be used to control the position of the acceptor in the assembly, allowing for the potential to build complex electron transfer cascades.

Designing amphiphilic assemblies with controlled structure to facilitate excited state electron transfer

2019 Fall National Meeting

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