Theoretical and Experimental Explorations of Charge Transfer in Small Molecules and Peptide Nucleic Acids

Non-adiabatic charge transfer (CT) is one of the simplest but very important chemical reactions. As a model system, alkanedithiols are among the most popular ones for short- or medium-range CT. Peptide nucleic acid (PNA), which consists of nucleobases and peptide backbones, is another promising model system for long-range CT. Various models and computational methods have been developed to describe three major experimental configurations: electrochemical measurement with self-assembled monolayer films (SAMs), single-molecule conductance measurement and photoinduced electron transfer (PET).;This dissertation have employed above methods to study the two model systems. The first work focuses on electrochemical models. Single-step models are widely used for analyzing CT through SAMs. However, long-range CT can occur in a "hopping" regime that involves multiple events. This study describes a three-step kinetic scheme to model CT in this regime. It is corroborated by the experimental results of a 10-mer PNA. The second study compares single molecule conductances of alkanedithiols and alkoxydithiols. Both molecular junction measurements and theoretical simulations by non-equilibrium Green's function (NEGF) method show that the conductance is lower for alkoxydithiols and the difference is length dependent. A pathway analysis of the electronic coupling is used to explain the results. The last two studies address the importance of conformational distributions on CT in PNAs: The third study compares the electrochemical charge transfer rates of normal aeg-PNA and gamma-PNA which has a less flexible backbone. Theoretical simulations show that the greater flexibility of the aeg-PNA gives rise to a more frequent appearance of high-CT rate conformations. In the last study a new PNA scaffold with a [Ru(Bpy)3]2+ donor and a bis(8-hydroxyquinolinate)2 copper acceptor for PET is described. Experiments show that whether the [Ru(Bpy) 3]2+ is terminally or centrally situated affects PET. Molecular dynamics simulations reveal that the difference in conformational distributions is a possible explanation. The above findings provide a deeper understanding of CT in molecules, and may facilitate the development of non-adiabatic dynamics in a bigger picture.