Electrochromic tuning of transparent gold nanorods with poly[(3,4-propylenedioxy)pyrrole] shells in the near-infrared region

We report on electrochemically tunable hybrid nanostructures composed of gold nanorods encapsulated within directly polymerized poly[(3,4-propylenedioxy)pyrrole] (PProDOP) nanoshells with controlled nanoscale thicknesses. This system displays narrow visible-near infrared absorption bands upon applying a variable electric potential due to the remarkable transmissivity of PProDOP at various oxidation states. The PProDOP shells were synthesized by in situ chemical oxidative polymerization using a mild oxidizing agent. The PProDOP demonstrated outstanding electrochemical performance, such as reversible electroactivity, high transmissivity in the visible range at various oxidation states, as well as a low oxidation potential (−1.06 V vs. Fc/Fc+). We suggest that the stable reversible modulation of the observed plasmonic response of the gold nanorods was caused by the variation of the refractive index of PProDOP shells at different oxidation states as shown by spectroscopic ellipsometry and confirmed by finite-difference time-domain (FDTD) simulations. A surface plasmon resonance (LSPR) band of gold nanorods at 800 nm was shifted reversibly by 24 nm by multiple cycling of the electric potential. Overall, these core–shell structures with electrochemical plasmonic tunability in the near-infrared region allow for tailoring of the optical and electrochemical properties of pre-programmed plasmon responses for active control of colorimetric appearance not just across the visible range but also toward the near-infrared.