Single Nanoparticle Chiroptics in a Liquid: Optical Activity in Hyper-Rayleigh Scattering from Au Helicoids

Abstract

Linear optical methods of determining the chirality of organic and inorganic materials have relied on weak chiral optical (chiroptical) effects. Nonlinear chiroptical characterization holds the potential of much greater sensitivity and smaller interaction volumes. However, suitable materials on which to perform measurements have been lacking for decades. Here, we present the first nonlinear chiroptical characterization of crystallographic chirality in gold helicoids (≈150 nm size) and core/shell helicoids with the newly discovered hyper-Rayleigh scattering optical activity (HRS OA) technique. The observed chiroptical signal is, on average, originating from between ≈0.05 and ≈0.13 helicoids, i.e., less than a single nanoparticle. The measured HRS OA ellipticities reach ≈3°, for a concentration ≈10 9 times smaller than that of chiral molecules with similar nonlinear chiroptical response. These huge values indicate that the helicoids are excellent candidates for future nonlinear chiroptical materials and applications.

Pathways to increase the dissymmetry in the interaction of chiral light and chiral molecules

“…Such behaviour holds significant promise in the development of new spectroscopic methods to interrogate chiral substances that exhibit a low dissymmetry. [1][2][3][4] Whether such approaches have broader impact in applications exploiting light-matter interactions remains to be seen.…”

“…The interaction of CP light with chiral molecules (and vice versa) underpins a range of spectroscopies already routinely used to interrogate chiral substrates -(electronic/vibrational) circular dichroism (ECD, VCD), optical rotation/rotatory dispersion (ORD), Raman optical activity (ROA) -and continues to be of interest in cutting edge developments in the measurement sciences. [1][2][3][4] The aim to use CP light in asymmetric synthesis is a historically important example. As early as the 19 th century, it was suggested that CP light could be used for the selective production of an enantioenriched substance, and CP lightdependent photochemical reactions remain a candidate for the origin of the homochirality of life.…”

Recent Advances in Inorganic Chiral Nanomaterials

“…[59] The illumination volume in a sample cell (dispersing Au@SiO 2 core@shell helicoids III, with a size of ≈150 nm) was estimated to be ≈30 µm 3 , so that the HRS OA signals were collected from 0.05-0.13 of individual (or sub-single) helicoids. [60] The HRS has a wavelength of ≈375 nm under the 720-nm excitation, well above any other multiphoton emission; and the HRS intensities ( RCP…”

Selective Excitation of Polarization‐Steered Chiral Photoluminescence in Single Plasmonic Nanohelicoids

“…[ 14 ] In addition, the photothermal dichroism has also been realized by depositing plasmonic chiral NPs on a thin AlGaN: Er 3+ film, which exhibits both optical and photothermal chirality due to the circular differential absorption. [ 15 ] However, the physical mechanism for the GNH‐enabled chiroptical modulation remains unclear, though the single‐particle chiral scatterometry [ 16 ] and hyper‐Rayleigh scattering [ 17 ] of the GNHs in solution have been investigated. Further study on the chiral PL properties of the GNHs is expected to elucidate the relationship between excitation/emission circular polarization and the handedness of chiral emitters in many chirality‐related modulation and PL processes.…”