Synthesis and Investigation of Light Responsive Molecules Containing Cyclopropenium Ions
The present thesis describes recent advances in the pursuit of novel light-responsive molecules containing cyclopropenium ions. In an effort to understand the underlying factors regarding the photophysical properties of cyclopropenium ions, emphasis was placed on the previously reported “Janus sponge”, where systematic structural modifications to four individual components of the molecule led to measurable and predictable changes in molar extinction coefficients, quantum yields, and Stokes shifts. Using time-dependent density functional theory calculations, the origin of these trends were traced to internal charge transfer. Additionally, modulating hydrogen bonding between intermolecular, bifurcated, and intramolecular interactions by choice of counterion was used to alter the quantum yield of cyclopropenium ion-containing fluorophores. The basis of this switchability was examined using X-ray diffraction analysis, 1H NMR spectroscopy, density functional theory calculations, and fluorescence spectroscopy. Notably, this work led to the development of the first cyclopropenium ion containing “true” proton sponge. As an extension, light responsive molecules are not isolated to fluorescence. This thesis also outlines the development of the first cyclopropenium ion containing an azo group. Key findings include the fact that cyclopropenium ion containing azo compounds are stable and cyclopropenium ions red-shift the absorbance wavelength in comparison to azobenzene by 75 nm. The synthetic, structural, electronic, and photophysical properties of these compounds are discussed.