Photophysics and photochemistry of pyridine-bridged chromophores

Organic π-conjugated materials are growing in popularity as they can be employed in flexible devices such as OLED displays, used in bioimaging, and for sensing applications. The incorporation of heteroatoms, in particular nitrogen, provides a simple synthetic handle that can be used to modify organic emitters through reactions such as protonation, oxidation, alkylation, and chelation, leading to a new class of molecules with different photophysical properties. This thesis explores a series of pyridine-containing luminophores arranged in donor-acceptor architectures and the changes in the photophysical properties when functionalized at the nitrogen center. First, a spectroscopic study examines the effect of substituent size at the nitrogen on the conformational and rotational properties of the molecule. Modification of the nitrogen by protonation, oxidation and alkylation are investigated and differences in photophysical properties are observed. Substitutions with groups larger than a hydrogen induce restricted rotation in specific molecules resulting in atropisomerism. NMR, UV-Vis, and emission spectroscopies are used to explain the impact of different substitutions on fluorescence quantum yield. Next, a new photoreaction is demonstrated in which a C–N bond is formed between pyridine and different polyaromatic hydrocarbons (PAHs). Protonation and chelation of the pyridine enables compounds to react under UV irradiation. The mechanism of this photoreaction is explored using kinetic experiments, revealing a photochemically driven single electron transfer (SET) reaction. The scope of this reaction is tested with different chromophores, electron-withdrawing/donating groups and under various reaction conditions. The formation of the C–N bond leads to planarization and rigidification of the photoproduct, leading to a redshift in emission wavelength and an increase in fluorescence quantum yield.Science, Faculty ofChemistry, Department ofGraduat