The Causality of Circular Dichroism Inducement by Isotropic and Anisotropic Chiral molecules

Circular dichroism (CD) spectroscopy is widely used in the conformational analysis of biomolecules. The CD of chiral molecules is weak. Therefore, plasmon-generated near field is used to enhance the CD of chiral molecules. In this study, we propose a chiral molecule-nanodimer coupled system to investigate the CD enhancement that originates from molecular CD (CDmol) and induced CD (CDind). Calculation results show that CDind is generated from different optical rotations and attenuation rates of the near field under right circularly polarized (RCP) and left circularly polarized (LCP) light. In the case of oriented molecular assembly, CDind becomes twice that in the case of isotropic molecular assembly or even larger. Moreover, CDind acquires the maximum value when the orientation of the molecular assembly is parallel to the strongest component of the electric field. Different components of the electric field generate opposite CD, thereby reversing the CDind spectra. These findings can be helpful in realizing ultrasensitive probing for chiral molecules.