Oppositely charged, water-soluble polyelectrolytes undergo a spontaneous complexation and phase separation process, forming a dilute solution coexisting with a polymer-rich phase. This process has applications in fields spanning food science, origin of life studies, biomedicine, underwater adhesives, and general materials science. However, this associative phase separation behavior has been studied only minimally in <i>conjugated</i> polyelectrolytes (CPEs) –macromolecules analogous to chromophores found in light harvesting organelles. We recently showed that a single model CPE underwent phase separation when electrostatically complexed to a non-conjugated polyelectrolyte in a high-salt environment. We found that the nature of the cation choice influenced the radiative decay rate and the electronic excited state (exciton) diffusion dynamics within the highly polymer-rich dense phase. Our findings highlighted the importance of the interactions of the complex with ions differing in polarizability and size. In this work, for the first time we demonstrate the use of associative phase separation to construct a complex fluid composed of an exciton donor CPE and an oppositely charged exciton acceptor CPE. We show that within this complex fluid phase photoexcited donor CPEs undergo very efficient exciton transfer to the acceptor CPE, thereby forming a dense aqueous exciton-transport network. We report on the influence of a chemical series of molecular ions with varying degrees of unsaturation but similar size on the phase behavior and energy transfer of the CPE complex. We find that, at high ionic strength, molecular ions led to a transition from a two-phase system to an optically clear single phase – a transition that was not observed with similar concentrations of the simple salt, KBr. We further show that a nearly threefold increase in the excited-state lifetime accompanies the transition from the concentrated phase of the two-phase solution to the fully dissolved state in the high-salt-concentration limit. Thus, this phase transition leads to an increase in exciton delocalization and a decrease in the excited-state depolarization rate, as captured by time-resolved fluorescence anisotropy. Our results have implications for constructing complex light-harvesting systems in an environmentally benign manner.

Conjugated polyelectrolyte-based complex fluids as aqueous exciton transport networks

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.