Chiral optical materials exhibit distinct optical properties under right handed and left handed circularly polarized light, and may find application in metaphotonic devices, in spin-based systems, holography, or as sensors. This talk will focus on chiral structures that exhibit tunable circular dichroism, and are designed to interact with different polarization states from small changes to the structure.<br/>The first part of the talk will describe our recent work on chiral semiconductor nanocrystals. Chirality can be introduced into semiconductor nanocrystals via different routes, including from chiral ligands on the surface of the nanocrystal. However, the application of these materials in photonics is limited by the relatively low dissymmetry factors. Using post-synthetic ligand exchange, we synthesized a class of chiral CdSe nanocrystals with a variety of different chiral ligands bound to the surface. We first synthesized CdSe nanocrystals via non-hot injection methods, with native, achiral carboxylic acids on the surface. As synthesized, these nanocrystals do not exhibit any circular dichroism. Post-synthetic ligand exchange of the native ligands to chiral carboxylic acids results in circular dichroism spectra associated with the excitonic transitions of the CdSe nanocrystal. We examine a family of related carboxylic acid ligands, which reveal a 30-fold difference in dissymmetry factors, reaching as high as 7 x 10<sup>-4</sup>, and show how the structure of the ligands influences the resulting circular dichroism spectra.<br/>The second part of the talk will discuss chiral metamaterials that incorporate different materials systems. Many strategies to tune the circular dichroism of chiral metamaterials rely on mechanical reconfigurations to modify coupling. This talk will discuss a chiral metamaterial that interacts with different polarization states only by changing the refractive index of one component. The unit cell of this chiral metamaterial consists of both patterned plasmonic structures and patterned dielectric structures, designed so that they interact via scattering. Tuning the refractive index of the dielectric component reverses which polarization is predominantly absorbed by changing the relative absorption of one plasmonic rod compared to the other. This structure can be in conjunction with light emitters to induce circularly polarized luminescence.

Tunable chiral optical properties in semiconductor nanocrystals and metamaterials

2019 Fall National Meeting

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