Proton-transfer reactions in “super” photoacids and supramolecular assemblies

by T.S. Kumpulainen

Institution: Universiteit van Amsterdam
Year: 2015
Record ID: 1251488
Full text PDF: http://hdl.handle.net/11245/1.473480


Transfer of a proton is undoubtedly one of the most elementary and yet one of the most significant reactions in chemical and biological processes and have received great attention during the last 60 years. Surprisingly, the exact mechanism of this elementary reaction is still not fully understood especially in non-aqueous environments. Photoacids, compounds that increase their acidity upon excitation, have enabled detailed time-resolved studies of the proton dissociation process. This thesis explores proton-transfer reactions in “super” photoacids and in supramolecular assemblies using steady-state and time-resolved spectroscopy. We start by introducing a novel class “super” photoacids and explore their acid-base and spectroscopic properties in aqueous solutions. We explain the origin of the photoacidity and demonstrate how it can be influenced. Secondly, we present a combined computational and experimental study of intermolecular proton-transfer reaction in organic solvents. Our findings suggest that the proton-transfer mechanism is much more complex in the absence of water and the kinetics are heavily influenced by the solvent properties such as polarity, viscosity and proton conductivity. The second half of the thesis focuses on proton transfer in supramolecular assemblies. First, we show how proton transfer can be utilized to convert photon energy into mechanical motion. This is achieved by using molecular machines where the proton transfer induces a nanometer-sized structural rearrangement on a nanosecond time scale. Secondly, we explore intramolecular proton transfer in an organocatalyst and show how a detailed understanding of the photophysical properties can be used to gain insights into the catalytic mechanism of these catalysts.