MANIPULATION OF LIGHT AND ELECTRONS WITH SUBMOLECULAR RESOLUTION
Laura Rios, Nick Tallarida, Joonhee Lee, Ara Apkarian.
University of California, Irvine, Irvine, CA.
Recent spectroscopic experiments reveal machinations of single-molecule chemistry with sub-molecular spatial resolution. This presentation encompasses highlights from 2 major experiments, introducing viewers to single-molecule chemistry and exploring the frontiers of the field as technological applications become apparent. Both experiments have significant implications in hetereogenous catalysis, which we hypothesize is the most important physical problem to be elucidated. It is clear that out of many catalytic sites, few offer catalytic activity. In our experiments, it is clear that the presence of a catalytic site (e.g., an adatom on the surface) may not necessarily provide the catalytic activity for the reaction (isomerization) to take place. Therefore, it is important to study these systems to gain insight into catalytic physics. In both experiments, a scanning tunneling microscope (STM) was used to image the molecules and manipulate their electronic environments. Our ultimate goal was to observe single-molecule, tip-enhanced Raman spectroscopy (TERS). Initially, we injected electrons into a porphyrin derivative to create a Jahn-Teller active anion. The electron density was visualized as the molecule underwent a conductance switch. These experiments have implications in molecular electronics. In the second set, an azobenzene derivative was interrogated spectroscopically with a 532 nm laser. Our results included 2 distinct, anti-correlated spectra, suggesting 2 forms of the molecule existed in mutual exclusivity, and indicating single-molecule behavior. We came away with several innate questions of light-adsorbate interaction such as the catalytic role of the nano-metallic junction of the STM, and the origin of selective, large shift of the Raman spectra.