UC Berkeley

Solution processable materials offer a variety of exciting possibilities, owing to their low-costand ease of tunability. Many next-generation electronic devices are being developed using solution processable materials, but their performance is typically hindered by the complex heterogeneous structures that result from their assembly or deposition. The characteristic length scales of this heterogeneity are typically nanometers and micrometers, and time scales of interest for material function can vary by many orders of magnitude (e.g., femtoseconds to minutes) depending on the context. In this dissertation, we employ a suite of time-resolved spectroscopies and microscopies to address material dynamics relevant for the transport of (excitation) energy and mass.

Chapter 2 describes measurements characterizing the excited state evolution of a proteinboundchromophore intended for a biomimetic photosynthetic light harvesting complex using transient absorption spectroscopy. These measurements employ a series of chromophoreprotein chemical linking groups that vary in their length and rigidity, which enables control over the chromophore-protein coupling. The findings here inform design principles for biomimetic light harvesting systems as well as the underlying photophysics potentially employed in natural photosynthetic systems for efficient excitation transport.

Chapter 3 describes correlative widefield single-particle tracking and atomic force microscopy(AFM) phase imaging to determine how the nano- and microscale semicrystalline morphology in electrolytic poly(ethylene oxide) (PEO) thin films influences the motion of small particles. The findings here suggest that polymer crystallinity, if controlled well, need not necessarily be a detriment to the transport of small particle species despite this historically being a challenge for PEO solid-state electrolytes that are investigated as next-generation battery materials. Chapter 4 gives an overview of time-resolved ultrafast STED (TRUSTED), an ultrafast trans2 formation of STED super-resolution microscopy to track exciton migration at the nanoscale in optoelectronically coupled materials. TRUSTED takes advantage of well-defined optical quenching boundaries such that exciton displacements, even over small distances, will register as a change in the number of excitons quenched. We describe the basics as well as the nuances in trying to apply this method to a series of electronically coupled materials.

Finally, Chapter 5 will discuss the ongoing investigation, at the time of this writing, ofexciton transport in Tellurium doped CdSe/CdS core-shell quantum dot superlattices. We investigate exciton transport using TRUSTED as well as time-resolved emission spectroscopy (TRES) and single-particle emission spectroscopy to characterize how the energetic disorder imposed by dopants modulates exciton transport. Steps to finish this work are detailed, which involve reconciling the time-rate of exciton energy decay measured by TRES with the exciton diffusivity measured by TRUSTED.

Taken together, this dissertation illustrates specific examples of characterizing materialstructure-function relationships across a variety of different systems. To do so, it requires using a number of different characterization tools, and, in each case, reveals the importance of matching the scale of the experimental length and/or time resolution to the native length and time scales of material structural heterogeneities and dynamics, respectively.