Helical Magnetic Field-Induced Real-Time Plasmonic Chirality Modulation

Abstract

The astrophysical phenomenon of mimetic helical magnetic field (h B)-assisted self-assembly is herein introduced to build helical superstructures that display chiroptical properties. As a building block, magnetoplasmonic (MagPlas) Ag@Fe3O4 core–shell nanoparticles are used to guide plasmonic Ag nanoparticles onto a helical magnetic flux. The chirality of the assembled helical structures and tailored circular dichroism are successfully tuned in real time, and the handedness of the assembled structures is dynamically switched by the h B at the millisecond level, which is at least 6000-fold faster than other template-assisted methods. The peak position of circular dichroism can be reconfigured by altering the plasmonic resonance or coupling by controlling the size of the Ag core and magnetic flux density. The h B-induced chirality modulation represents a method to control the polarization state of light at the nexus of plasmonics, magnetic self-assembly, colloidal science, liquid crystals, and chirality. It presents active and dynamic chiral assemblies of magnetoplasmonic nanomaterials, enabling further practical applications in optical devices.

Chiral plasmonic nanostructures: recent advances in their synthesis and applications

“…214 Another example makes use of a helical magnetic field to assemble magnetoplasmonic Ag@Fe 3 O 4 core-shell nanoparticles into chains stacked in a chiral nematic-like superstructure that can be dynamically modulated at the millisecond time scale. 215 Chirality can also be obtained by stacking layers of in-plane oriented 1D nano-objects or 1D assemblies with a twist, leading to so-called Bouligand structures. Using a very elegant and simple approach, Probst et al have recently shown that twisted chiral assemblies can be prepared from spherical gold nanoparticles (Fig.…”

Recent Advances in Inorganic Chiral Nanomaterials

“…Displayed colors can be dynamically tuned using helical magnetic field (hB), which was applied to dynamically transfer electromagnetic chirality to magnetoplasmonic Ag@Fe 3 O 4 NPs through the dynamic formation of helical superassemblies. [24] The helical superassemblies show engineerable CD signals as a function of the field strength and frequency of hB, to obtain full-color tuning capability with no need of a color filter. As a result, the hB-induced dynamic chirality transfer paves the way toward producing thin display panel with high light efficiency.…”

“…[5] Chiral driving forces are indispensably applied to impose chirality onto inorganic NPs, which have been reviewed previously. [6][7][8] Chiral driving forces include chirality transfer from chiral ligands, [9][10][11] chiral templates [12] (such as DNA, [13] proteins, [14] peptides, [15] cellulose nanocrystals, [16] liquid crystals modified with chiral ligands, [17] lipidic nanoribbons, [18] chiral mesoporous silica, [19] nanohelices [20,21] ), circularly polarized light (CPL), [22] spatially chiral arrangement using lithography techniques, [23] helical magnetic fields, [24] orbital angular momentum, [25] macroscopic asymmetric gradients of biaxial strain fields, [26] and macroscopic shear forces. [27,28] A pair of chiral objects are designated as enantiomorphs, and especially a pair of chiral molecules are called enantiomers.…”

Engineering of inorganic nanostructures with hierarchy of chiral geometries at multiple scales

“…Indeed, the phenomenon of helical magnetic field ( h B )‐driven symmetry breaking of light was used to induce self‐assembly of magnetoplasmonic Ag@Fe 3 O 4 core‐shell NPs (diameter of the Ag core is ~61.4 nm and the Fe 3 O 4 shell thickness is ~54.3 nm.) (Figure 13A) into helical superstructures with tailored, tunable, and switchable chiroptical properties in real‐time 156 . In Ag@Fe 3 O 4 NPs, Fe 3 O 4 magnetic shell was used to guide plasmonic materials onto the magnetic flux.…”

“…Adapted with permission from Ref. 156 Copyright © 2020 American Chemical Society. (E) chiral colloidal clusters assembled from asymmetric dimers under alternating current electric fields (peak‐to‐peak voltage V pp = 11 V and ω = 600 Hz): (1) large field of view of chiral tetramers.…”