Chemistry Colloquium: Dr. Michael Ruggiero

The Department of Chemistry in the College of Arts and Sciences is pleased to welcome Dr. Michael Ruggiero, an Associate Professor at University of Vermont.

Title: Terahertz Spectroscopy: A Powerful Tool for Characterizing Organic Semiconducting Solids

Abstract
Over the past two decades, terahertz time-domain spectroscopy has become a valuable technique for the characterization of solid samples, primarily due to its sensitivity to bulk molecular packing arrangements. However, in recent years the role that specific terahertz vibrations play in a number of important physical phenomena has become increasingly apparent, with numerous studies highlighting how terahertz motions are directly responsible for the proper functioning of materials, ranging from enzymatic catalysis to solid-state phase transformations. Such dynamics are intimately linked to the molecular structures, condensed phase geometries, and even individual atomic details (e.g. electronic configuration), and therefore understanding material properties is intrinsically linked to understanding the associated low-frequency dynamics. In this work, the nature of terahertz-frequency motions in molecular solids, coupled with state-of-the-art ab initio quantum mechanical simulations, will be used to interpret, characterize, and predict a number of physical characteristics related organic semiconducting solids. Specifically, the role of terahertz phonons in determining the type and nature of dynamic disorder in organic semiconducting crystals will be highlighted, with specific attention paid to understanding the nature of the forces that result in exceptionally large electron-phonon couplings and thus hinder charge carrier mobilities in such materials. This work will showcase how this methodology enables the resolution of dynamic disorder on a mode-by-mode basis, thereby providing a framework for future work on optimizing organic semiconductors on the basis of a ‘phonon-engineering’ approach. The understanding gained through terahertz spectral characterization is currently enabling the guided and rational design of new materials, ultimately showcasing the utility of terahertz spectroscopy for the complete characterization of advanced materials.