There is significant interest in developing molecular, light-harvesting systems that efficiently convert photon energy into chemical potential energy. The optimal system would be prepared using environmentally benign materials, be able to absorb a large portion of the solar emission spectrum and be able to efficiently move excited states toward an active interface. In this report, we demonstrate the formation of an aqueous, hierarchically assembled system consisting of an energetic exciton funnel templated on the surface of lipid vesicles (liposomes) and oriented from the outside towards the membrane interior. To do this, we embed a lipophilic phthalocyanine exciton acceptor in the liposome and subsequently adsorb a conjugated polyelectrolyte (CPE) exciton donor on the outer surface. We then adsorb a secondary CPE at the outer interface to form a structure that exhibits a ternary exciton funnel and that displays absorption across the entirety of the visible spectrum. We show that, although energy transfer is efficient, the assembly morphology depends sensitively on preparation conditions and relative ionic stoichiometry. We argue that the electrostatic correlation energy likely plays an important role in understanding such complex formation, leading to evidence that a CPE Wigner liquid is an intermediate state in the assembly. This proof-of-principle study exposes important parameters that must be considered when constructing and optimizing such a system. Our results advance understanding of how to form an environmentally benign, panchromatic light-harvesting system.

Towards panchromatic exciton funnels via liposome scaffolds of conjugated polyelectrolytes

ACS Spring Meeting 2021

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