A laser trapping-spectroscopy study on the photocyanation of perylene across a single micrometre-sized oil droplets/water interface: droplet-size effects on photoreaction quantum yield

Abstract

Photoirradiation of perylene in the presence of 1,4-dicyanobenzene and NaCN in a benzonitrile (BN)/water emulsion under vigorous stirring gave 1- and 3-cyanoperylene in a total yield of 15%. For kinetic and mechanistic studies of the photoreaction, we conducted single-droplet measurements by using a laser trapping-microspectroscopy technique. Although determination of the incident light intensity absorbed by a solute in the emulsion is in general very difficult owing to strong light scattering, that in single laser-trapped BN droplets dispersed in water was successful on the basis of the photooxidation reaction of 9,10-disubstituted anthracene. The quantum yield of the photocyanation of perylene (Φ_CN) was then determined to be 4.9 × 10⁻³. Furthermore, we found that Φ_CN was linearly proportional to the inverse of the droplet radius: the reaction efficiency increased with decreasing droplet size through an increase in the surface area/volume (A/V) ratio of a droplet. This is the first demonstration of micrometre droplet size effects on the quantum yield for a photoreaction across the droplet/water interface.