Global energy challenges demand inexpensive, environmentally friendly artificial light-harvesting materials. Artificial light harvesting using self-assembled, light weight<i> soft </i>materials is attractive for converting sunlight into chemical potential energy. Ideally, the system should exhibit spectrally broad light absorption, directional electronic energy transfer (EET), long-lived charge generation, and spatial partitioning of the interior. We have previously shown that oppositely charged conjugated polyelectrolytes (CPEs) can be ionically assembled into aqueous complexes that readily undergo EET from the donor to the acceptor in less than 250 fs. Can such light-harvesting EET antennae be spatially partitioned to create mimics of membraneless light-harvesting organelles? In this work, we interrogated the spontaneous phase-separation of model CPE complexes with the goal of understanding how the solution ionic strength couples to the exciton dynamics of the complexed CPEs. For the first time, we have used rheological measurements to confirm formation of CPE-based complex coacervate phases as a function of excess monovalent ions. We find that the nature of the simple cation with a fixed bromide counterion has a large influence on the phase behavior. Furthermore, we show that the CPE exciton diffusion dynamics change qualitatively both as a function of salt concentration and as a function of cation type, indicating a significant coupling between ionic and electronic degrees of freedom. Our results suggest that salt-induced phase separation in CPE-based systems holds substantial promise for the construction of light-harvesting membraneless organelle mimics.

Towards artificial light-harvesting organelle mimics: Exciton dynamics in conjugated polyelectrolyte complex coacervates

2019 Fall National Meeting

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