Circular Dichroism Generation Research Articles

Generation of Circular Dichroism from Superposed Magnetically Oriented Magnetic Nanoparticles

Circular dichroism (CD) spectra were observed for the doubly superposed film–film and solution–solution samples, which all contained magnetically oriented achiral iron oxide magnetic nanoparticles (MNPs). The observed CD spectra critically depended on the angle difference, Δθ, between the orientation axes of MNPs in the superposed samples, giving the maximum CD value at the angle of Δθ = 45°. In a single solution cell sample with doubly superposed magnetic fields also, similar CD spectra depending on the angle difference between the magnetic fields were observed. These observed CD spectra were successfully reconstructed from the observed linear dichroism (LD) and linear birefringence (LB) spectra of each sample by the use of a superposed Mueller matrix method. Furthermore, triply and quadruply superposed solution samples exhibited the maximum CD spectra at the angle differences of Δθ = 30 and 22.5°, respectively, as suggested by the superposed Mueller matrix calculation. Thus, the origin of all CD spectra observed for the superposed achiral MNP samples has been quantitatively assigned to the helical combinations of LD and LB spectra of the magnetic field-induced optically oriented MNPs.

Generation of circular dichroism from superposed porphyrin films.

Circular dichroism (CD) was observed from the superposed porphyrin deposited glass plates, which were prepared by the vapor deposition of achiral porphyrin molecules and oriented to one direction by rubbing parallel to the surface of plate. The CD spectra depended on the twisted angle between the plates and the number of plates superposed. The observed CD spectra agreed with the simulated ones by the Mueller matrices superposition calculation using the observed linear dichroism spectra and linear birefringence spectra of each plate.

Femtosecond laser-induced circular dichroism in silica: Dependence on energy and focusing depth

Abstract The paper addresses the creation of strong circular dichroism from a femtosecond laser light with a linear polarization strongly focused in silica glass and perpendicular incidence. All aspects of the experiment are therefore achiral and should not give rise to chiral property creation if taken themselves alone. We investigate the laser-induced circular dichroism according to orientation of the laser polarization, pulse energy and focusing depth. It appears that deep focusing under high numerical aperture conditions leads to higher ellipticity when compared to shallow focusing or low numerical aperture focusing. Strong circular dichroism can be imprinted when polarization is at ±45° of the horizontal scanning direction in reference to the laser plan. In addition the generation of circular dichroism appears to be closely related to the spatial aberration, spatial chirp and beam elongation under strong focusing conditions.

Fabrication of chiral plasmonic oligomers using cysteine-modified gold nanorods as monomers

Generation of circular dichroism (CD) beyond the UV region is of great interest in developing chiral sensors and chiroptical devices. Herein, we demonstrate a simple and versatile method for fabrication of plasmonic oligomers with strong CD response in the visible and near IR spectral range. The oligomers were fabricated by triggering the side-by-side assembly of cysteine-modified gold nanorods. The modified nanorods themselves did not exhibit obvious plasmonic CD signals; however, the oligomers show strong CD bands around the plasmon resonance wavelength. The sign of the CD band was dictated by the chirality of the absorbed cysteine molecules. By adjusting the size of the oligomers, the concentration of chiral molecules, and/or the aspect ratio of the nanorods, the CD intensity and spectral range were readily tunable. Theoretical calculations suggested that CD of the oligomers originated from a slight twist of adjacent nanorods within the oligomer. Therefore, we propose that the adsorbed chiral molecules are able to manipulate the twist angles between the nanorods and thus modulate the CD response of the oligomers.

Mechanisms of the generation of circular dichroism of singlet-triplet transitions

Possible mechanisms of the generation of circular dichroism of singlet-triplet transitions localized in achiral chromophores are investigated in this work. The estimates show that the spin-orbit interaction of the optical electrons in the field of the electrons and nuclei of the perturbing groups (the “external”l-s interaction) makes a contribution comparable in order of magnitude to the “internal.”