Orthogonal Light-Induced Self-Assembly of Nanoparticles using Differently Substituted Azobenzenes

Precise control of the self-assembly of selected components within complex mixtures is a challenging goal whose realization is important for fabricating novel nanomaterials. Herein we show that by decorating the surfaces of metallic nanoparticles with differently substituted azobenzenes, it is possible to modulate the wavelength of light at which the self-assembly of these nanoparticles is induced. Exposing a mixture of two types of nanoparticles, each functionalized with a different azobenzene, to UV or blue light induces the selective self-assembly of only one type of nanoparticles. Irradiation with the other wavelength triggers the disassembly of the aggregates, and the simultaneous self-assembly of nanoparticles of the other type. By placing both types of azobenzenes on the same nanoparticles, we created unique materials ("frustrated" nanoparticles) whose self-assembly is induced irrespective of the wavelength of the incident light. A guiding light: Nanoparticles functionalized with variously substituted azobenzenes self-assemble into aggregates in response to different wavelengths of light. Exposing a mixture of differently sized nanoparticles, each functionalized with a different azobenzene, to light of a specific color (ultraviolet or blue) induces the selective self-assembly of only one type of the nanoparticles. Irradiation with the other wavelength triggers the disassembly of the aggregates and the simultaneous self-assembly of nanoparticles of the other type.