The development of luminescent materials that are sensitive to both optical and electrical stimuli is of high interest for the fabrication of future information-processing devices. In this study we report about a novel fluorescent molecular switch (1) that can be light- and redox-controlled. This compound has been synthesized by covalent tethering of a perylenediimide fluorophore (PDI) to a dithienylethene (DTE) unit. The photochromic properties of the DTE group are preserved in the dyad, which can be reversibly converted between open (1o) and closed (1c) states upon irradiation. In addition, 1 displays electrochromicity, and its ring-opening process can be promoted quantitatively by electrochemical oxidation. Whereas the open-ring state of the switch is highly fluorescent, the emission of the PDI group in 1c is quenched by energy transfer to the DTE group. This allows large fluorescence modulation between the two states of 1, which can be operated either as an all-optical switch or by a combination of photo- and electrochemical stimuli. © 2012 American Chemical Society.