Laser trapping-microspectroscopy study on photochemical reactions in single oil droplets

Droplet-size effects on the photochemical reaction processes in single microdroplets and across a droplets/solution interface were studied based on a laser trapping-microspectroscopy measurement. First, a laser trapping-microspectroscopy-high pressure cell system was developed to elucidate the molecular-level mechanisms of the droplet-size effects. Second, pressure-induced droplet-size effects on the dimer formation efficiency of a surface active dye at a single droplets/water interface were studied. Third, the characteristics of an optical cavity effect on the energy-transfer dynamics in single microdroplets under high pressure were investigated. The results of single-droplet measurements under high pressure indicated that the droplet/water interfacial structures are very important factors governing the photochemical and photophysical processes. Fourth, a photocyanation reaction of pyrene in oil-in-water emulsion systems was investigated in terms of solvent, surfactant, droplet-size, and water solubility effects. Finally, a photocyanation reaction of perylene across a single microdroplets/water interface was studied. As the most important results, the quantum yield of the photocyanation reaction was linearly proportional to the inverse of a droplet radius. The results are the first demonstrations for micrometer droplet-size effects on the quantum yield for a photoreaction across a droplet/water interface.