Two-photon activation of photoactive ligands bound to gold surfaces

Photoactive crosslinkers are useful tools for optically driven assembly of nano-particles. We report on the use of ultra-short laser pulses to affect localized photoreactions in o-nitrobenzyl-based photoactive ligands bound to a gold surface with thiol groups. The reaction is activated through a combination of thermal activation and two-photon absorption, while at higher power densities, ligands can be ablated from the surface through breaking of the gold-thiol bond. We will present data on the interplay of these three effects as a function of laser power and exposure time, and demonstrate assembly of nanoparticles onto optically patterned surfaces. Finally, we will discuss how this effect could be used to create well-defined nanoparticle assemblies where great binding-site selectivity can be obtained through the combination of high electromagnetic intensity enhancements at plasmon hotspots and the nonlinear scaling of photoactivation efficiency in two-photon absorption processes. We acknowledge financial support from the National Science Foundation and the Institute for Critical Technology and Applied Science.