Effects of Molecular Structure on Interfacial Electron Transfer Explained by Marcus Theory

Electron transfer is one of the fundamentally important reactions in physics, chemistry, and biology. Numerous chemical and electrochemical reactions require fast electron transfer between an electron donor and an acceptor to successfully convert energy from one form to another. In particular, interfacial electron transfer dyenamics at a substrate decorated with surface-bound dye molecules and immersed in an electrolyte containing redox molecules have obtained great attention, arising in dye-sensitised solar cells and catalytic systems. At such semiconductor-liquid interfaces, efficient conversion of photonic energy into accessible chemical (or electrochemical) energy is dependent upon fast electron transfer between photo-oxidised surface-bound molecules and mobile electron donor molecules dissolved in electrolytes. At the same time, a competitive back electron transfer process, which occur between the semiconductor substrate and the oxidised form of the redox electrolytes, needs to be blocked to prevent loss of photo-excited electrons. A well-studied critical factor affecting the electron transfer reactions is energy difference between the donor and acceptor molecules (driving force, G). However, studies on factors such as electronic coupling (HDA) and reorganisation energy (λ) that also significantly influence the interfacial electron transfer kinetics are in a relative scarcity, which could be due to the difficulty in keeping the ∆G effect unchanged while altering molecular structure. Therefore, the design of redox-active molecules are mostly limited in the redox cascade reaction schemes. The aim of this PhD thesis was to enhance the interfacial electron transfer between the surface-bound molecules and the redox-electrolyte molecules by enhancing electronic coupling (HDA). In specific, this thesis focuses on the molecular structures that affect HDA via intermolecular interactions such as alkyl-alkyl and electrostatic interactions between the donor and the acceptor molecules.