Achieving Highly Stable, Reversibly Reconfigurable Plasmonic Nanocrystal Superlattices through the Use of Semifluorinated Surface Ligands

Controlling stability, complexity and optical response of reversibly reconfigurable plasmonic nanocrystal superlattices is of critical importance for emergent optoelectronic technologies and can be achieved by engineering the chemical nature of the ligand shell. In this work, we experimentally explore how the design of surface ligands with semifluorinated alkyl chains impacts dynamic self-assembly of nanoparticles. A series of three promesogenic thiols was synthesized and grafted onto plasmonic nanocrystals via ligand exchange reaction. In all cases, after solvent evaporation, we obtained reversibly reconfigurable, thermally responsive assemblies. We examined these nanomaterials using a variety of techniques such as transmission electron microscopy, UV–vis, and small-angle X-ray scattering. We show that the number of aromatic rings and the length of the fluorinated chain strongly affects symmetry and reconfiguration temperatures of the assemblies. For an optimized material we show that it is possible to achieve relatively quick switching between 3 distinct long-range ordered phases, including nonclose packed structures. Using numerical simulations, we confirm that observed plasmonic response of the material comes from the reconfiguration process. Uniquely, we confirm durability of the material in a 400 cycle switching experiment. Overall, these results guide our understanding of influence chemistry of the ligands on reversible reconfiguration of nanocrystal superlattices.