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Summary: Photosensitive microcapsules that reversibly switch upon visible light irradiation are attractive targets for drug delivery, fragrance release and pesticide delivery. In this study we report the development of visible light triggered microcapsules and demonstrate the concept of protection and remote release of a model, non-toxic perfume oil. Polyamide microcapsule shells containing visible light-sensitive ortho-substituted azobenzene moieties in the main chain of the polymer were prepared by oil-in-water interfacial polymerization method. Microcapsules surface and cross-section morphologies were observed by SEM. Triggered perfume release during light irradiation was monitored by means of GC/MS. We suggest that the mechanism of perfume release from the microcapsules shell is based on decrease of modified azobenzene length during light illumination. This visible light-induced compression of microcapsules offers a new way to modulate the release of encapsulated materials.

Novel functional polymeric microcapsules, based on modified azobenzene moieties, are exhaustively investigated, both from a theoretical and experimental points of view. Theoretical calculations and several measurements demonstrate that visible light can act as a trigger for release of encapsulated material, as a consequence of trans-cis isomerization which modifies microcapsule surface topography and can induce a “squeezing” release mechanism. Interfacial polymerization of an oil-in-water emulsion is performed and leads to core-shell microcapsules which are characterized by means of atomic force microscopy (AFM), optical microscopy (OM), scanning electron microscopy (SEM) and light scattering. These analyses put into evidence that microcapsules’ size and surface morphology are strongly affected by irradiation under visible light: moreover, these changes can be reverted by sample exposure to temperatures around 50°C. This last evidence is also confirmed by NMR kinetic analyses on modified azobenzene moiety. Finally, it is shown that these smart microcapsules can be successfully used to get a controlled release of actives such as fragrancies, as a consequence of visible light irradiation, as confirmed by an olfactive panel.

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