A Low-Symmetry Cubic Mesophase of Dendronized CdS Nanoparticles and Their Structure-Dependent Photoluminescence

A liquid crystal (LC) phase with P213 symmetry, the lowest so far in a cubic LC, was obtained in a system of CdS quantum dots (QDs) modified with a two-layer corona of aliphatic thiols (inner) and LC aromatic dendrons (outer). We propose that the unusual low symmetry of this cubic mesophase is a result of the multilayered corona, which prefers to adopt an anisotropic radial profile because of the combination of long and short "bristles.'' The anisotropic distribution of dendrons (long bristles) in the P213 phase is thought to facilitate pi-pi interaction among the aromatic moieties. The interaction gives rise to non-radiative exciton energy-transfer pathways that induce photoluminescence quenching of the CdS QDs. This is believed to be the first example of structure-dependent emission-quenching behavior.