Nondestructive Probing of a Photoswitchable Dithienylethene Coupled to Plasmonic Nanostructures

Abstract

We demonstrate the read-out of the conformational state of photoswitchable molecules, without modifying that state by the read-out process itself. The ring-opening and ring-closing reactions change not only the absorption spectrum of a molecular layer but also its index of refraction. A thin layer of a dithienylethene derivative was combined with well-designed gold nanostructures. The particle plasmon resonance of these nanostructures is extremely sensitive to the photoinduced change in the environment and can therefore be used to probe the state of the photochromic switch. The probing wavelength now interrogates the plasmonic structure, not the molecular film, and can thus be conveniently placed in a transparent spectral range, e.g., the near-infrared. We find good agreement between experiments and numerical simulations with regard to spectral signatures of the plasmon resonance.