Cecilia Noguez: Chirality and Optical Activity at the Nanoscale

Chirality, the asymmetric property of non-superposable mirror images, is present in molecules and compounds that are essential for life. Chirality also exists in inorganic systems at the nanoscale. Chiral objects are optically active and exhibit electronic circular dichroism (CD) in the same electromagnetic region where absorb light. CD is capable of measuring small differences in extinction between right and left circularly polarized light, which makes it a very sensitive tool to distinguish asymmetries. Understanding how to control chirality and increase the limits of CD spectroscopies would have significant impact in pure and applied sciences; providing a powerful tool for exploring and controlling chirality!dependent phenomena, including circular dichroism, templated enantioselective–growth in stereochemistry, electronic spin filters in spintronics, among other fields. In this talk, the mechanisms that originate and control optical activity in nanoscale systems such as organic-metal hybrid NPs and twisted bilayer graphene (TBLG) are identified using a time-perturbed density functional theory. In the first case, CD is studied in terms of the intrinsic chirality of the ligands, the number of ligands and the induced chirality by the arrangement of the chiral and achiral ligands in the NP. The analysis of CD allows the identification of the spectral regions where the induced chirality by the ligand array dominates over the intrinsic chirality, determining conditions for the control and enlargement of CD. In the second case, the experimental realization of thin films with full control of the structural handedness down to the atomic scale, which is possible by stacking two graphene layers whose chiral properties are designed by an interlayer rotation angle is also investigated. These results would be significant in the discussion of experimental CD spectra, which allow the development of new strategies to improve the sensitivity of chiroptical spectroscopies.