Molecular Steganography Using Multistate Photoswitchable Hydrazones

Abstract

The development of photochromic compounds that can have multiaddressable and -stable states is desirable for imparting multistate responses in soft materials. Here, we report on two such photochromes, composed of para-NO₂- and pentafluoro-phenyl functionalized hydrazones connected nonsymmetrically through an isosorbide linker, which exhibit highly efficient, orthogonal, and sequential switching. We took advantage of these properties and the multistability of the four different isomeric states (i.e., ZZ, ZE, EZ, and EE) to control the photophysical properties of nematic liquid crystals (LCs). Doping the switches into 5CB, followed by switching to the EE state, triggered an unusual cholesteric to focal conic phase transition. We used this property to modulate the opacity of the LC films, resulting in a molecular steganography application.