Bistable and Water-Operable Hemiindigo Photoswitches Allow Optical Control of Acetylcholinesterase Activity with Visible Light

While photopharmacology enables precise spatiotemporal control over drug activity, its widespread reliance on UV-responsive molecules often hinders preclinical and clinical advancements. Thus, alternative scaffolds can offer promising advantages over the commonly used azobenzene family. In this study, we introduce the first hemiindigo-based photopharmacological agents, which are capable of isomer-dependent human acetylcholinesterase inhibition in the nanomolar range. These hemiindigo photoswitches exhibit highly favorable properties: They are fully functional in aqueous medium with good photoisomerization quantum yields, respond exclusively to blue-to-orange visible light (415–590 nm), and maintain high stability in their metastable form, even in physiological buffers. Notably, indoxyl N-methylation emerged as a key structural feature for optimizing photophysical properties, as demonstrated through crystallography and a theoretical model describing the photochemical pathways governing photoisomerization. Overall, this study paves the way for broader exploration and future applications of the largely overlooked hemiindigo scaffold in photopharmacology.