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

Abstract

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 longrange 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.

Size-Dependent Thermo- and Photoresponsive Plasmonic Properties of Liquid Crystalline Gold Nanoparticles

“…These were indexed as (002), (011), (004), and a pair of (013) and (110) signals, assuming a tetragonal body-centered unit cell with unit cell parameters c ≈ 12.8 nm and a ≈ 4.2 nm. These observations were in agreement with the already shown tendency of liquid-crystalline-like ligand coated NPs to adopt this symmetry [27,36,42] as well as interparticle spacing. Surface-to-surface distance of neighbor NPs is~0.9 nm along the a direction, and 3.7 nm, along the unit cell diagonal direction.…”

“…The phase sequences of such materials and their structural parameters are strictly dependent on the interplay between the nanoparticle core and the structure of ligands. Several hybrid materials, reconfigurable between ordered lamellar, columnar, cubic, and other types of phases with short-or long-range ordering were obtained [32][33][34][35][36][37].…”

“…It is crucial given that the deformation of the nanoparticles' shape is required for anisotropic self-assembly. In this regard, it should be mentioned, that most of the up-to-date reports on liquid-crystalline phases made of nanoparticles require narrowing the size distribution of nanoparticles (often below 10%) through size-exclusive purification methods [36,39,42,43]. Consequently, the final synthetic yields are relatively low.…”

Gold Nanoparticles Thin Films with Thermo‐ and Photoresponsive Plasmonic Properties Realized with Liquid‐Crystalline Ligands

“…Utilization of liquid crystals has been a promising approach . Combining the optical properties of nanoparticles with the structural adaptability of liquid crystal (LC) systems has allowed the development of switchable materials .…”

“…Covering the surface of nanoparticles with properly designed LC ligands yields systems able to form nematic, smectic, and complex 3D structures . It was shown that the melting of LC affects the plasmonic properties of the material (i.e., causes the shift of SPR wavelength), therefore significant effort was directed at controlling the organization of nanoparticles by temperature . However, obtaining fast‐reacting or remotely controlled materials require use of stimuli other than temperature.…”