Electrically Controlled Plasmonic Behavior of Gold Nanocube@Polyaniline Nanostructures: Transparent Plasmonic Aggregates

We demonstrate the electrically controlled and reversible plasmonic signature of hybrid polymer–metal nanostructures composed of core/shell nanostructures: gold nanocubes (AuNCs) coated with electrochromic polyaniline (PANI) shells. A reversible tuning of the localized surface plasmon resonance (LSPR) peak of the AuNC core was obtained by applying an electrical potential that caused a reversible oxidation state change in the electroactive PANI nanoshell. A significant shift of the main LSPR peak was achieved with high reversibility and electrochemical stability due to the interplay of the local decay of the electromagnetic field and the controlled thickness of the surrounding polymer shell. Here, the PANI shell acts as an electroactive medium as well as a physical spacer to prevent uncontrollable plasmonic coupling. The most efficient LSPR shift can be induced by the refractive index change of nanoscale PANI shell thickness lower than the electromagnetic field decay length of the given gold nanoparticles. Single particle studies showed that coupling of plasmon resonances of densely packed nanocubes with thicker PANI shells was prevented and the extinction signature of individual core/shell nanocubes remained mostly unchanged after their assembly into densely packed aggregates. Therefore, these core/shell structures could preserve the original plasmonic signature of individual nanostructure by damping plasmonic coupling between AuNC cores.