Light-responsive self-assembly of semi-conducting nanoplatelets

Abstract

CdSe nanoplatelets are a recently discovered class of colloidal semiconducting nanocrystals. Atomic control over their thickness allows achieving control over quantum size effects, and in particular, these platelets exhibit monochromatic light emission because of the confinement of photo-generated excitons only in their thickness. These nanoplatelets can self-organize into supra-particular polymers, depending on their environment, which means that their shape anisotropy can be expressed at the microscale. Here, the self-assembly of semiconducting nanoplatelets is controlled remotely by light, in a dynamic nanoparticulate system that integrates light-responsive molecular switches covalently. Azobenzene ligands were thus designed to (i) be grafted on the nanoplatelets (ii) ensure their colloidal stability in chloroform when confined on their surface in the E-configuration. Upon irradiation, the ligands isomerize into their Z-configuration, leading to a modification of the dipolar moment of the particles and to the formation of one-dimensional stacks. The self-assembly is reversible, as thermal relaxation of the ligands yields the initial dispersion back. This reversible hybrid system can be used in the design of responsive optical systems, as illustrated by photo-patterning experiments leading to controlled spatial resolution of the luminescence intensity in thin films.