Resolving Optical and Catalytic Activities in Thermoresponsive Nanoparticles by Permanent Ligation with Temperature-Sensitive Polymers

Thermoresponsive nanoparticles (NPs) represent an important hybrid material comprising functional NPs with temperature-sensitive polymer ligands. Strikingly, significant discrepancies in optical and catalytic properties of thermoresponsive noble-metal NPs have been reported, and have yet to be unraveled. Reported herein is the crafting of Au NPs, intimately and permanently ligated by thermoresponsive poly(N-isopropylacrylamide) (PNIPAM), in situ using a starlike block copolymer nanoreactor as model system to resolve the paradox noted above. As temperature rises, plasmonic absorption of PNIPAM-capped Au NPs red-shifts with increased intensity in the absence of free linear PNIPAM, whereas a greater red-shift with decreased intensity occurs in the presence of deliberately introduced linear PNIPAM. Remarkably, the absence or addition of free linear PNIPAM also accounts for non-monotonic or switchable on/off catalytic performance, respectively, of PNIPAM-capped Au NPs.