Generation of Circular Dichroism from Superposed Magnetically Oriented Magnetic Nanoparticles

Abstract

Circular dichroism (CD) spectra were observed for the doubly superposed film−film and solution−solution samples, which all contained magnetically oriented achiral iron oxide magnetic nanoparticles (MNPs). The observed CD spectra critically depended on the angle difference, Δθ, between the orientation axes of MNPs in the superposed samples, giving the maximum CD value at the angle of Δθ = 45°. In a single solution cell sample with doubly superposed magnetic fields also, similar CD spectra depending on the angle difference between the magnetic fields were observed. These observed CD spectra were successfully reconstructed from the observed linear dichroism (LD) and linear birefringence (LB) spectra of each sample by the use of a superposed Mueller matrix method. Furthermore, triply and quadruply superposed solution samples exhibited the maximum CD spectra at the angle differences of Δθ = 30 and 22.5°, respectively, as suggested by the superposed Mueller matrix calculation. Thus, the origin of all CD spectra observed for the superposed achiral MNP samples has been quantitatively assigned to the helical combinations of LD and LB spectra of the magnetic field-induced optically oriented MNPs.

Intrinsic Design and Modulated Circular Dichroism of Inorganic Nanowire/Hydrogel Composite

“…[ 11 ] Our group has also demonstrated several methods for generating structural chirality with magnetoplasmonic (MagPlas) nanostructures as building blocks, including colloidal core–shell nanospheres of Ag@Fe 3 O 4 , [ 12 ] and self‐assembled films of core–shell nanowires of Au@Fe x O y . [ 13 ] Recently, Watarai and Takechi [ 14 ] proved that circular dichroism can also be generated by chirally superposed linear structures, which do not require the individual layers of meta‐assemblies to be in close vicinity of each other. From the abovementioned cases, a common approach to generating circular dichroism from achiral building blocks is stacking multiple 1D aligned layers with a manual twist angle, which is both cumbersome and limited in terms of layer counts.…”