Building Complexity in Soft Light-Harvesting Systems via Phase Separation of Semiconducting Polyelectrolytes

Seminar | March 17 | 2-3 p.m. | 277 Cory Hall

Speaker/Performer:  Prof. Alexander L. Ayzner, UC Santa Cruz, Chemistry & Biochemistry

Sponsor:  Berkeley Nanosciences and Nanoengineering Institute

There is a substantial need for soft, electronically active materials in a variety of applications, such as sensing, artificial skin, biomedical devices, and light harvesting. Water-soluble semiconducting polyions – or conjugated polyelectrolytes (CPEs) – have emerged as promising materials for such applications due to their attractive combination of optoelectronic and self-assembly properties. One of the more fascinating aspects of non-conjugated polyelectrolyte materials is their phase behavior, leading to a diversity of soft matter such as complex fluids, hydrogels, and viscoelastic liquids.

In this talk I will focus on our lab’s efforts to use phase separation of CPEs to form light-harvesting soft materials in aqueous media. We have recently shown that CPE-based complex fluids based on oppositely charged exciton-donor and exciton-acceptor CPEs give rise to highly efficient electronic energy transfer as well as a strong coupling between electronic and ionic degrees of freedom. This is attractive from a light-harvesting perspective, since the nature of the ionic environment can be used to manipulate the polyelectrolyte photophysics.

However, CPE-based viscoelastic liquids (called coacervates) have proved elusive, as the average CPE’s propensity to form extensive π-stacking interactions strongly favors the solid or solid-like macrostate. The ability to form a CPE-based coacervate has intriguing light-harvesting implications: Such a state would in principle allow for substantial electronic connectivity while supporting molecular diffusion.

I will show how our lab very recently solved this problem by rationally designing a chemical series of CPEs which have for first time been demonstrated to undergo liquid/liquid phase separation in water. This insight has allowed us to form the semiconducting coacervate state. I will describe our current understanding of the mechanism that drives CPE coacervation and the emergent excitonic states that form in the process.
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Alex Ayzner did his PhD at UCLA and postdoc at Stanford SLAC. Awards include the NSF CAREER and the Hellman Fellowship. He joined the faculty at UCSC in 2014.

Event Contact:  victorr@eecs.berkeley.edu, 510-643-6681

Access Coordinator:  Avi Rosenzweig,  victorr@eecs.berkeley.edu,  510-643-6681