Hydrazone Switches and Things in Between

This feature article surveys the various ways by which a structurally simple hydrazone can be used in accessing different functional materials, mainly photo/chemically activated switches, fluorophores and sensors. The modularity of this functional group enabled us to develop new switching mechanisms, pathways, cascades and loops, while addressing challenges in the field, such as waste accumulation, how to control cross-talk between different types of switches, developing photochromic compounds with benign activation wavelengths, among others. All of these advances are expected to play, in one permutation or another, an important role in the coming decades in the field of molecular switches and machines.