Active metamaterial absorber by photoswitchable molecules

Active or intelligent materials whose properties are governed by an external stimulus have been used for many application including memories, opto-electronic devices, smart windows, drug delivery, bio-analytics, and surgery, amongst others. Not only transition metal oxides, semiconductors, and smart polymers have been shown to be applicable as switchable materials, molecular switching elements attracted the attention for the same purposes, too. In particular, molecule-plasmon interacting systems are very promising alternative to replace traditionally used active compounds. Combination of great potential of photo-active molecules with astonishing capability of plasmonics could open up new way in smart materials. In a molecule-plasmon hybrid system, the plasmonic resonance peak can be adjusted (shifted, split, or its intensity can be tuned) through the externally induced changes in the molecule. Although this concept has been widely explored, the application oriented approach is still missing. Recently, we have demonstrated that combination of the absorbing character of the photo-switchable dye molecules and plasmon resonance allows realization of a novel type of optical system, wherein the optical transparency can be manipulated by illumination. Visibly irradiated polymer doped spirooxazine which covered the thin metal film shows high transparency (higher than the intrinsic transparency of bare metal film) while UV exposure of the samples immediately turn the sample opaque. High electrical conductivity of the metal film and molecular induced transmission enhancement of the film enables us to have a transparent conductive metal with controllable optical transparency (smart material). With the same strategy, we also have shown that an optically driven perfect absorber can be developed in a multilayer films with few 10th of nanometer thickness. In such system, the reflectivity (absorption) of the metal mirror could be dropped down (increased) to a few percent (100%) or recovered to more (less) than 95% (5%) dynamically by UV or visible illumination, respectively.