Thioketal-photocage: a universal modification strategy for constructing new photochemical tools for real-time imaging in living cells.

Photoactivable fluorescent probes (photocages) are powerful tools for studying biological processes in living cells. We report a novel class of photodegradable thioketals that serve as photo-responsive elements and apply them to xanthene dyes to design photocages for live cell imaging. Compared with traditional thioketals, these compounds demonstrate the ability to undergo deprotection upon exposure to ultraviolet-visible light, independent of photosensitizers or external oxidants and relying solely on dissolved oxygen within the solvent. This photoreaction results in a remarkable 68-fold increase in fluorescence intensity. We verify that the uncaged product is the corresponding ketone, with high-performance liquid chromatography analysis, which indicates a yield of up to 80%. Furthermore, we extend this modification strategy to xanthene dyes substituted with various heteroatoms and confirm the universal applicability of this photoactivable strategy. These dyes exhibit good stability against reducing agents and metal ions, with carbon and silicon xanthene photocages also demonstrating commendable dark stability against reactive oxygen species. We apply these photocages for bioimaging and further modify them for selective labeling, activation, and imaging of specific organelles and intracellular proteins within living cells. This modification strategy offers high spatiotemporal selectivity and holds promise as a powerful tool for advanced biological studies.