Photochemically triggered assembly of composite nanomaterials through the photodimerization of adsorbed anthracene derivatives

Gold nanoparticles were assembled into three-dimensional aggregates in colloidal dispersions and were attached to ZrO₂ surfaces through photoinduced [4 + 4] cycloaddition reactions between adsorbed anthracene derivatives. Composite materials were characterized by ultraviolet/visible/ near-IR spectroscopy, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Aggregates of gold nanoparticles with diameters of several micrometers were formed within 45 min of illumination at 355 nm and 130 mW/cm². Aggregation was attributed primarily to interfacial photodimerization between anthryl groups on different gold nanoparticles, although intramonolayer photodimerization reactions may also have occurred. 9-Anthracenethiolate-capped gold nanoparticles were attached to 2-anthroate-functionalized ZrO₂ surfaces upon excitation of anthryl π-π* transitions. ToF-SIMS data and the results of control experiments suggested that the materials assembly mechanism involved [4 + 4] cycloaddition reactions between adsorbed anthryl groups on gold and ZrO ₂. Patterned arrays of nanoparticles with ∼100-μm features were deposited onto surfaces. The use of interfacial photodimerization reactions to trigger materials assembly processes may represent an attractive materials fabrication strategy, in which photopatterning (top-down) and nanoparticle-adsorption (bottom-up) processes proceed via a single photoinduced reaction.