Bidirectional plasmonic coloration with gold nanoparticles by wavelength-switched photoredox reaction.

Reversible tuning of localized plasmon resonance that is supported by nanometric-sized metal particles holds potentially huge benefits in terms of manipulating light for widespread photonic applications. Although the practice of altering the frequency and the amplitude of plasmon resonance on gold nanoparticles is relatively well established, dynamic tuning by all-optical approaches for coloration has long been hindered due to limited implementation approaches with which gold nanomaterials can be photosynthetically manipulated. Here, we develop a wavelength-switched photoredox approach and demonstrate bidirectional tuning of the plasmonic resonance of crystalline gold nanoparticles for reversible surface-plasmon-resonance-based coloration. The reversible plasmonic resonance control is achieved by a combination of photoreduction of gold ions and photooxidation of gold nanorods by switching the illumination between UV and near-UV-Vis light, respectively. As one example, the plasmon resonance peak of gold nanorods is reversibly tuned between 630 and 660 nm by switching the light wavelengths. Utilizing wavelength-switchable photoredox reactions, we demonstrate reversible color patterning by mask illuminating a gold nanorod sample solution. This approach offers not only an easy-to-implement method for realizing non-contact modulating plasmon-resonance based colors, but also new opportunities for reversibly tuning local plasmon resonance by all-optically shaping single nanoparticles. This holds great potential for a wide range of applications, including active-substrate-based surface-enhanced Raman scattering (SERS), erasable optical data storage and dynamic laser color printing, among others.