  We present a rigorous finite element method to calculate circular dichroism
(CD) in various systems consisting of nanostructures and oriented chiral
molecules with electric quadrupole transitions. The interaction between
oriented molecule materials, which are regarded as anisotropic chiral media,
and metallic nanostructures has been investigated. Our results show that the
plasmon-induced CD is sensitive to the orientations of the molecules. In many
cases, the contribution of molecular electric quadrupole transitions to the
total CD signal can play a key role. More interesting, we have demonstrated
that both the quadrupole- and dipole-based CD signals can be improved greatly
by matching the phases for the electromagnetic fields and their gradients at
different regions around the nanostructures, which are occupied by the oriented
chiral molecules. Different regions might produce CD of opposite sign. When
integrating over regions with only one side of the proposed nanostructure, we
find that the CD-peak may be nearly hundreds-fold over the case of integrating
both sides. We believe that these findings would be helpful for realizing
ultrasensitive probing of chiral information for oriented molecules by
plasmon-based nanotechnology.
