The role of plasmonic excitations in the optical activity of periodic structures with configurational chirality

Abstract

Broken mirror symmetry of chiral structures imposes a lack of mirror symmetry in the scattering profile. When an energy dissipation channel is introduced in the system, an overall optical activity arises. Plasmonic nanostructures, therefore, are an ideal platform to induce optical activity by means of constitutional or configurational chirality. We experimentally investigate the mechanism of plasmonically induced configurational chirality in a periodic monoclinic hole array with a broken mirror symmetry. The resulting optical activity of the structure is studied by using k-space leakage radiation measurements.

Directional Plasmonic Excitation by Helical Nanotips

“…One can notice a very clear helical structure of the measured maps with opposite handedness, which we link to the strong symmetry breaking by the tips. In chiral system, two enantiomers can be interconverted by a spatial inversion rather than by a time reversal [34,35]. As we observed, also the k-space CD maps geometrically behave as two enantiomers.…”

“…Following these observations of spin-dependent SP behavior, we decided to investigate the circular dichroism induced by the chiral tips. As is well known, chiral structures exhibit optical activity manifested by the differential absorption of circular light states [ 34 ]. This effect leads to a measurable ellipticity of the incident linearly polarized light and can be directly derived by separately measuring the transmission of circular polarization states as follows: where I R and I L are the intensities for right and left polarization, respectively, and is the ellipticity angle.…”

Directional Plasmonic Excitation by Helical Nanotips

“…One can notice a very clear spiral structure of the measured maps with opposite handedness which we refer to the strong symmetry breaking by the tips. In chiral system, two enantiomers can be interconverted by a spatial inversion rather than by a time reversal [29,30]. As we observed, also the k-space CD maps geometrically behave as two enantiomers.…”

“…Following these observations of spin-dependent SP behavior we decided to investigate the circular dichroism induced by the chiral tips. As is well known chiral structures exhibit optical activity manifested by the differential absorption of circular light states [29]. This effect leads to a measurable ellipticity of the incident linearly polarized light and can be directly derived by separately measuring the transmission of circular polarization states as follows:…”

Supramolecular Chirality in Azobenzene-Containing Polymer System: Traditional Postpolymerization Self-Assembly Versus In Situ Supramolecular Self-Assembly Strategy

“…Configuration refers to the permanent geometry of molecules with spatial arrangement connected by covalent bonds, while conformation refers to the different arrangement of atoms (or groups) in molecules due to free bond rotation under certain conditions. Configurational chirality ( Figure 2 a) comes directly from the covalent arrangement of the molecular structure, which cannot be changed without breaking the covalent bond [ 38 ]. The most basic form of configuration chirality is point chirality.…”