Ultrafast investigation of light-driven electron proton transfer in intermolecular model systems

This dissertation investigates Electron-Proton Transfer (EPT) and other excited state reaction kinetics in organic molecule systems. This work was done with the goal of gaining a better understanding of the interrelated motions of electrons and protons in excited state molecular systems. Ultrafast spectroscopy techniques were used to monitor the excited state dynamics on the time scale they are occurring. Chapter 1 provides an introduction to EPT, the research, and the important chemical properties that affect these excited state dynamics. A review of recent literature on proton coupled electron transfer and electron proton transfer is included in Chapter 2. Chapter 3 describes the experimental techniques used for the experiments in this dissertation.;Chapter 4 presents the spectroscopic evidence for photo-EPT in nitrophenyl-phenol. Femtosecond transient absorption measurements show energy dependent pathways for the nitrophenyl-phenol-base adduct. At high energy excitation there are two pathways: (1) a photo-EPT transition where the molecule is excited to an elongated proton transfer state, and (2) a trapped proton state, where the molecule undergoes a singlet-triplet intersystem crossing and the proton is transferred from the triplet nitrophenyl-phenol molecule to the base. At low energy excitation only the photo-EPT state is observed.;Chapter 5 describes the ultrafast photo-EPT that gives rise to the increased emission of hydroxycoumarin in aqueous or basic solutions. Our spectroscopic data also show base concentration dependent tautomerization in the excited molecule. In the presence of excess base femtosecond transient absorption measurements and time-correlated single-photon counting experiments can chart the progress as the phenolic proton is shuttled across the molecule forming a neutral excited state tautomer.