Induced Chirality through Electromagnetic Coupling between Chiral Molecular Layers and Plasmonic Nanostructures

Abstract

We report a new approach for creating chiral plasmonic nanomaterials. A previously unconsidered, far-field mechanism is utilized which enables chirality to be conveyed from a surrounding chiral molecular material to a plasmonic resonance of an achiral metallic nanostructure. Our observations break a currently held preconception that optical properties of plasmonic particles can most effectively be manipulated by molecular materials through near-field effects. We show that far-field electromagnetic coupling between a localized plasmon of a nonchiral nanostructure and a surrounding chiral molecular layer can induce plasmonic chirality much more effectively (by a factor of 10(3)) than previously reported near-field phenomena. We gain insight into the mechanism by comparing our experimental results to a simple electromagnetic model which incorporates a plasmonic object coupled with a chiral molecular medium. Our work offers a new direction for the creation of hybrid molecular plasmonic nanomaterials that display significant chiroptical properties in the visible spectral region.

Surface-Enhanced Circular Dichroism of Oriented Chiral Molecules by Plasmonic Nanostructures

“…[6][7] A weak molecular CD signal in the ultraviolet spectral region can be both enhanced and transferred to the visible-near-infrared region when chiral molecules are adsorbed at the surfaces of metallic nanoparticles or in the nanogaps (i.e., hot spots) of particle clusters. However, many related discussions assume that the molecules are randomly oriented, 6,[21][22][23][24] and the results have been obtained by averaging over the solid angles of the molecular directions. In fact, this rotational degree of freedom for molecules is absent in many cases, i.e.…”

Enantioselective control of lattice and shape chirality in inorganic nanostructures using chiral biomolecules

“…Several mechanisms were suggested for induction of chiroptical phenomena in such systems (both metallic and semiconducting). In plasmonic nanosystems the dipolar nearfield interaction 7 , or a far-field electromagnetic coupling 8,9 between a metal nanoparticle and a chiral molecule could lead to induction of CD in the plasmon resonance as well as enhancement of the molecular CD by the near-field coupling 10,11 . These effects, which may be useful for biomolecular sensing 9,12 and are fundamentally interesting, are nevertheless limited in magnitude.…”

“…In plasmonic nanosystems the dipolar nearfield interaction 7 , or a far-field electromagnetic coupling 8,9 between a metal nanoparticle and a chiral molecule could lead to induction of CD in the plasmon resonance as well as enhancement of the molecular CD by the near-field coupling 10,11 . These effects, which may be useful for biomolecular sensing 9,12 and are fundamentally interesting, are nevertheless limited in magnitude. Stronger effects could be obtained in systems of achiral nanoparticles arranged in a chiral superstructure with strong interparticle interaction [13][14][15][16] .…”

Angular momentum-induced circular dichroism in non-chiral nanostructures

“…However, recent experiments with planar mirror-symmetric plasmonic structures have shown that a non-zero CD can be obtained if the sample is illuminated at oblique angles [10][11][12][13] . Other attempts to create CD with a non-chiral sample have been carried out surrounding the sample with a chiral medium [14][15][16] .…”