Directed Assembly of Gold Bipyramids and Quantum Dots Using Click Chemistry for Plasmon-Exciton Coupling

Advances in directed nanoparticle assembly are enabling the development of hybrid nanostructures with enhanced light-matter interaction. Among these hybrid nanostructures are those with coupled plasmonic and excitonic components. Here, we report the design and assembly of hybrid nanostructures for plasmon-exciton coupling, composed of end-to-end pairs of gold bipyramids (AuBPs) with a CdSe/CdS quantum dot (QD) between the AuBPs. The assembly is achieved through a copper-free click reaction between azide-functionalized AuBPs and dibenzocyclooctyne (DBCO)-modified QDs, providing efficient and strong linkage between nanoparticles. The functionalization and assembly of the nanoparticles was verified through infrared and visible absorption spectroscopy, fluorescence spectroscopy, zeta potential measurements, and transmission electron microscopy. The AuBPs provide concentrated electric field confinement at their tips through the excitation of longitudinal plasmon resonances, enabling interaction with excitons in QDs located near the tips. Measurements on single assemblies showed an induced transparency in the plasmon scattering spectrum, characteristic of intermediate coupling between plasmons and excitons. A coupling strength of 45 meV was achieved for single QDs at room temperature. These results highlight the potential of colloidal AuBP-QD assemblies for achieving strong plasmon-exciton coupling using a directed assembly approach enabled by an efficient click chemistry strategy.