Chirality Induction at the Helically Twisted Surface of Nanoparticles Generating Circularly Polarized Luminescence

Circularly polarized luminescence (CPL) can be generated either from fluorescent dyes with chiral structures or from achiral luminophores in chiral environments such as chiral hosts or chiral self-assemblies. Herein, we demonstrate the CPL induction to an achiral fluorophore grafted on an inorganic nanoparticle (NP) with a chiral shape. NPs composed of a mercury sulfide (HgS) cinnabar phase with a chiral crystal structure are investigated as a platform on which the achiral molecules self-assemble into a chiral arrangement. Both the crystallographic and morphological chiralities of HgS NPs are independently considered for the induction of a chiral arrangement of achiral dyes. The HgS NPs with an ellipsoidal shape (nanoellipsoids) are modified with the achiral fluorescent dye, resulting in no CPL emission. The larger HgS NPs with a chiral twisted structure (nanotwists) are found to give rise to CPL. The sign of CPL signals could be regulated through the modification of the twist direction of the HgS NPs. Chirality is considered to be induced in the arrangement or assembly of achiral fluorescent molecules on the chirally twisted surface of NPs.