Figure 3: CD splitting theory and comparison to experimental results.
From: Chiral plasmonic DNA nanostructures with switchable circular dichroism
(a) Scheme of L-NHs aligned orthogonal and parallel to a polarized light beam. The possible CD excitation modes are indicated with double arrows (red, CDz; blue, CDxy). (b) The simulated peak-dip CD signal of randomly oriented L-NHs can be composed by the superposition of weighted transverse CDz and longitudinal CDxy signals. The directional CD signal (CDz or CDxy) is much stronger than the signal originating from randomly dispersed helices as averaging over the orientation of the chiral objects typically strongly reduces the CD signal. (c) Simulated CD spectra for helices oriented at angles restricted to a cone with a given opening angle θ. (d) The CDz (red curve) and the CDxy (blue curve) were measured from the same ensemble of L-NHs by switching the orientation of the L-NHs (cf. Fig. 2). The black curve shows the calculated superposition of weighted CDz and CDxy. Importantly, this curve resembles the CD signal of nanohelices dispersed randomly in solution. Note that the peak shift between the inverted modes (indicated by the grey vertical lines) is larger than expected from theory (as indicated in b). This can be attributed to differences of the refractive indices of the particle-surrounding media in dry and wet samples.
