Interest in the synthesis of chiral nanostructures has been fueled by their prime fundamental and potential application of chiral nanostructures in biosensing, telecommunication, display technologies, diffraction-free patterning, and chiral catalysis. Although chirality is often associated with biochemistry due to numerous chiral biomolecules, today chiral inorganic nanostructures have attracted much attention, but their optical properties remain largely unexplored. Nanoscale inorganic chiral materials strongly rotate linear and circularly polarized light passing through them. Such optical effects are relatively easy to observe and are being actively investigated as a part of the study of chiral photonics and plasmonics. However, the opposite effects, the transfer of spin angular momenta of circularly polarized photons to materials and their subsequent nanoscale restructuring, are much less understood.
In chapters II and III of this dissertation, I describe an experiment that demonstrates how circularly polarized light (CPL) affects dispersions of racemic nanoparticles (NPs). The intrinsic, non-covalent electrostatic, dipole-dipole, and van der Walls interactions, as well as hydrogen bonds between NPs combined to produce different types of NP superstructures. The transition from individual NPs to their superstructure assemblies can be easily controlled, visualized, and studied by different means. This strategy was applicable to various materials such as gold. By illuminating a seed-free gold ion dispersion with CPL, I could obtain optically active gold nanostructures.
In chapter IV, I describe how I synthesized chiral cobalt oxide NPs using chiral molecules, namely, L- and D-cysteine as surface ligands. The chiral paramagnetic NPs showed ~ 10 times greater optical activity than other metal or semiconducting NPs of similar size. Moreover, the optical activities of the latter were mainly in the UV region while our NPs show practical activity in both the UV and visible ranges. The results of this study provide new opportunities for the design and synthesis of novel materials and contribute to a better understanding of materials at the nexus of magnetism and chirality.PHDMacromolecular Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/140792/1/jyeom_1.pd
