Rational Design of Intrinsically Semiconducting Coacervates via Aqueous Liquid/Liquid Phase Separation of Conjugated Polyelectrolytes

About This Grant

With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Dr. Alexander Ayzner of the University of California, Santa Cruz will determine the molecular characteristics that govern the structure and electronic properties of liquids that have both viscous and elastic properties, called coacervates, composed of conjugated (semiconducting) polyelectrolytes (CPEs). Such liquids are promising candidates to serve as aqueous photochemical reactors and compartments in artificial photosystems that mimic natural photosynthesis. To develop a foundational understanding of such systems, the influence of ions on the nature of the electronic states and their movement within the system will be interrogated across a series of CPE structures using a combination of thermodynamic and optical techniques. Once the fundamental characteristics that govern such states of soft matter are determined, artificial reaction centers will be incorporated into the CPE coacervates to improve their light harvesting characteristics. The lifetime of the charged carriers and the efficiency of their generation will be elucidated using a combination of optical characterization techniques. This research will develop the next generation of STEM professionals by training graduate and undergraduate students, as well as promising high school students via the state-wide California science summer school program. CPEs exhibit fascinating aqueous phase behavior that spans the viscoelastic continuum from solids to complex fluids and, as shown more recently, coacervates. The relatively large CPE concentration within the coacervate leads to significant excitonic connectivity, and the liquid nature of this macrostate allows for diffusion of small molecules. These characteristics are highly promising for aqueous light-harvesting systems. However, there exists no fundamental physical-chemical understanding of how spatially extended π-stacking interactions and the coupling between electronic and ionic degrees of freedom conspire to determine the stability and properties of intrinsically electronic coacervates – viscoelastic liquid phases that are highly enriched in CPE chains. In this project the strength of ion-π interactions and the ion hydration free energy will be correlated with the nature of emergent electronic states and the exciton diffusion within the coacervate. The influence of extended π-stacking interactions on the stability, structure, and electronic structure of the coacervate phase will be determined by systematically varying the CPE backbone topology. Having characterized the fundamental structure/property relationships that underpin electronic coacervates, the ability of such phases to support the formation of long-lived photoinduced electron/hole pairs will be studied. Doing so will generate new fundamental knowledge regarding the mechanistic aspects of liquid-liquid phase separation of CPEs for the formation of coacervates and lead to the ability to rationally design coacervate droplets that serve as light-harvesting compartments in complex aqueous photosystems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.