(363i) Chiral Templating of Self-Assembling Nanostructures By Circularly Polarized Light

Examples of chemical reactions affected by spin angular momenta of circularly polarized photons are rare and display low enantiomeric excess.  High optical and chemical activity of nanoparticles (NPs) should facilitate the transfer of spin angular momenta of photons to nanoscale materials. However, such processes are currently unknown.  Here we demonstrate that circularly polarized light (CPL) strongly affects self-assembly of racemic CdTe NPs.  Illumination of NP dispersions with right- and left-handed CPL is shown to induce the formation of right- and left-handed twisted nanoribbons, respectively.  Enatiomeric excess of such reactions was found to be greater than 30% which is ~10x higher than other CPL-induced reactions.  In contrast, illumination with linearly polarized light and assembly in the dark led to straight nanoribbons.   The mechanism of “templation” of NP assemblies by CPL is associated with selective photoactivation of chiral NPs and clusters followed by their photooxidation.  Chiral anisotropy of interactions translates into chirality of the assembled ribbons. Their strong optical activity is confirmed by ensemble measurements, single ribbon CD spectroscopy, finite element modeling of the chiroptical properties based on Maxwell equations, and atomistic molecular dynamic simulations.  The ability of NPs to retain polarization information, or the “imprint” of incident photons opens new pathways for the synthesis of chiral photonic materials and allows for better understanding of the origins of biomolecular homochirality.