Using Low Energy Light to Enable High Energy Photochemistry

Abstract: Manipulating light to meet human needs is pivotal in various research fields and technological applications, ranging from solar energy conversion to photodynamic therapy and fluorescence imaging of cells and tissues. This thesis addresses the spectral mismatches between available light and the specific energy requirements of target photochemical reactions by employing low-energy light to control high-energy photochemistry. Central to this endeavor are molecular photoswitches, represented by diarylethene and spiropyran derivatives, which serve as model compounds across all discussed papers. The experimental research presented herein explores three distinct methodologies: rapid fluorescence modulation, triplet sensitization, and triplet-triplet annihilation photon upconversion. Notably, the rapid modulation of fluorescence using a water-soluble diarylethene derivative enables the differentiation of fluorescence from a bright background, opening up for contrast-enhanced fluorescence imaging in cellular environments. Additionally, the realization of all-visible-light switching of diarylethenes through nanocrystal/molecular hybrid triplet sensitizers enhances the fatigue resistance of the diarylethene molecules. Furthermore, the investigation into triplet-triplet annihilation photon upconversion reveals promising avenues for single-wavelength control of diarylethenes and water-compatible photochemistry, demonstrated by the isomerization and deprotonation of a spiropyran photoacid. While triplet sensitization relies on close molecular contact between light-manipulating species and photoreactants, photon upconversion allows for physical separation due to photons serving as energy carriers. Building upon these advancements, further optimization and mechanistic understanding are necessary for these methods to realize their full potential. Nevertheless, the findings presented in this thesis bring us closer to achieving visible-light control of high-energy photochemical transformations, offering significant implications for both fundamental research and practical applications.