Thermo- and photoresponsive reversible changes in localized surface plasmon resonance of gold nanoparticles covered by poly(N-isopropylacrylamide) with photochromic diarylethene end group

Thermoresponsive poly(N-isopropylacrylamide) (poly(NIPAm)) with a diarylethene (DE) chromophore at the end group (DE–poly(NIPAm)) was synthesized by reversible addition-fragmentation chain transfer polymerization. The resulting polymer has a lower critical solution temperature at 33 °C and exhibits photochromism in water upon photoirradiation. Gold nanoparticles covered with DE–poly(NIPAm) were prepared by malate reduction, followed by the addition of DE–poly(NIPAm) with SH at the ω-end group. The localized surface plasmon resonance band of the gold nanoparticles exhibits a bathochromic shift with heating and photoirradiation. This is ascribed to changes in the refractive index by the shrunken dehydrated state and the photochromic reaction of the DE chromophore with heating and photoirradiation, respectively.