Plasmon-Induced Circular Dichroism of a Chiral Molecule in the Vicinity of Metal Nanocrystals. Application to Various Geometries

The Coulombic interaction between a chiral molecule and a non chiral metal nanocrystal creates new plasmonic lines in a circular dichroism (CD) spectrum. In many cases, optical lines in CD spectra of chiral molecules and plasmon absorption bands in metal nanocrystals are not in resonance. Typically, CD lines of chiral molecules are in the UV spectral range, whereas plasmon bands of metal nanocrystals are in the visible range. Nevertheless, plasmon excitations can strongly interact with dipoles of chiral molecules and become chiral. We demonstrate this effect theoretically and derive a general equation for the CD spectrum of a complex composed of metal nanocrystals and a single chiral molecule. In our theory, new plasmon peaks in the CD spectra come from an effect of interference between external and induced fields inside a hybrid complex. Our models involve single spherical nanoparticles, nanoparticle pairs, and nanoshells. The results obtained here can be used to design new optical materials and hybrid nanosystems with sensor properties.