Enhanced One-Photon Cycloreversion Reaction of Diarylethenes near Individual Gold Nanoparticles

The photocycloreversion reaction of a diarylethene upon irradiation with visible light was found to be accelerated in proximity to a gold nanoparticle covered with diarylethene polymers (Au-poly(DE)) dispersed in a solution. Enhancement of the reaction rate by the gold nanoparticle was quantitatively evaluated by kinetic analysis on the basis of absorption spectroscopy. Multicomponent bleaching of the closed-ring form of poly(DE) was observed around the gold nanoparticle upon irradiation with visible light; the irradiation time dependence of the absorbance could be explained using a reaction model with two decay components rather than one. The results indicate that the cycloreversion reaction was enhanced only in the vicinity of the gold nanoparticle. The faster reaction inside the polymer shell was confirmed by numerical spectral simulation of Au-poly(DE) using a double shell model based on Mie theory. The enhancement factor determined as the ratio of the enhanced reaction rate to the nonenhanced rate was estimated to be 2−5, and the enhanced region was evaluated to be 9−12 nm from the surface of the gold nanoparticle. The enhancement factor tended to increase with irradiation at longer incident wavelength, which did not correlate with the spectral shape of the local surface plasmon resonance (LSPR) band of the gold nanoparticle.