Applications of Optical Spectroscopy in Studies on Energy and Electron Transfer and Solvation Effects in Nanoscale and Molecular Systems

This thesis describes three investigations, ranging in subject matters, all of which relating to systems capable of photoinduced reactions involving energy or electron transfer. The phenomenon and the effects of environment in the various systems are explored using different methodologies of optical spectroscopy. As the chapters progress, different investigations introduce and build on fundamental concepts encountered and in complexity of the methodologies used to explore the systems. The first chapter introduces the preparation of water-soluble CdSe nanocrystal clusters. The clusters, created using a protein, are 3-D close-packed self-assemblies of nanocrystals. Due to this close-packed nature, electronic interactions between the nanocrystals allow for energy migration within the cluster. The structural and optical properties of the clusters were described. Then using steady-state spectroscopy, properties of the original nanocrystals were compared to that of the cluster to determine the consequence of nanocrystal coupling interactions and their potential use toward the development of artificial light-harvesting systems. In the second chapter, CdSe nanocrystals are functionalized with a unique electro-active polymer, and the electron transfer between the nanocrystal and the electro-active polymer adsorbate is investigated. Using fluorescence decay measurements, the electron transfer reaction inherent to the system with respect to a comprehensive range of dielectric solvents was explored. The study illustrates the high complexity of seemingly typical nanocrystal-based systems and provides general awareness of what factors need to be considered when dealing with such systems. The final chapter starts with an informal review of ultrafast nonlinear spectroscopy, focusing on two methods, three-pulse photon echo peak shift (3PEPS) and two-dimensional photon echo (2DPE) electronic spectroscopy, and how they are related. A straightforward approach for extracting 3PEPS data from 2DPE results is presented in a preliminary case study of a dye in two different solvents, one of which is electron-donating.Ph