Caging-group-free photoactivatable fluorophores with far-red emission

State-of-the-art super-resolution microscopy methods benefit greatly when combined with photoactivatable or photoswitchable fluorophores with far-red emission, but the majority of these fluorophores require specialized buffers or rely on photolabile protecting groups that limit their biocompatibility. We report here a caging-group-free strategy for photoactivatable dyes based on 1-vinyl-10-silaxanthone derivatives containing 9-acylimino or 9-(alkoxycarbonyl)imino groups, enabling minimally sized photoactivatable dyes with ≥680 nm emission. The 9-(alkoxycarbonyl)imino silaxanthones are particularly suitable for live-cell labeling, undergoing byproduct-free photoactivation to yield bright and photostable fluorophores that can be readily imaged by STED (stimulated emission depletion), PALM (photoactivated localization microscopy), or MINFLUX (minimal photon fluxes) nanoscopy techniques. The labels derived from these photoactivatable dyes open up new possibilities for multiplexed imaging.