N-Heterocyclic carbene-ended polymers as surface ligands of plasmonic metal nanoparticles

A facile methodology to prepare N-heterocyclic carbene (NHC)-terminated polymers as surface ligands to functionalize gold nanoparticles (AuNPs) is reported. Our method highlights a mild, aerobic synthesis of NHC-functionalized polymers and a simple ligand exchange approach towards surface modification of AuNPs prepared in aqueous solution. Two methods, including end-group functionalization of halogen-ended polymers from a conventional atom transfer radical polymerization (ATRP) and post-polymerization functionalization of imidazole-containing polymers using imidazole-containing ATRP initiator, have been investigated to prepare imidazolium-ended polymers. Using a one-step, oxygen and moisture tolerant procedure, the polymer–NHC–Cu(I) species can be synthesized from imidazolium-ended polymers and readily bind to citrate-capped AuNPs likely through transmetalation, yielding robust polymer-stabilized AuNPs. Our synthetic method significantly simplifies the preparation and use of polymer–NHC ligands for surface functionalization of metal NPs. Our methodology is general and potentially applicable to any polymers prepared by ATRP to functionalize metal NPs via NHC–metal coordination; therefore, it will likely broaden the applications of polymer–NHC ligands for metal nanoparticles in the fields of catalysis and nanomedicine.