Visible-light activatable coumarin-based phototriggers for fluorescence imaging with ultra-high photolysis efficiency

Photoactivated fluorophores (PAFs) are powerful imaging tools for observing subcellular structures and tracking dynamic biological processes. However, photoremovable protecting groups (PPGs) widely used to construct PAFs suffer from the drawbacks of short-wavelength excitation and/or low photolysis efficiency. Herein, a class of coumarin-based PPGs with electron-rich thiophene derived substitutions at the C3-position of a coumarin scaffold were prepared. The modification not only leads to the redshift of the absorption band to the blue light region (400-500 nm), but also the increases of uncaging quantum yield (Φ_u) as well as molar extinction coefficient (ε_max), thus enhancing the photolysis efficiency (Φ_u × ε_max) up to 34.2 × 10³ M^-1 cm^-1. The exceptionally high photolysis efficiency enables efficient photolysis in blue light as weak as 2 mW cm^-2 or in blue light from a Luminol chemiluminescence system. Based on the excellent photolysis properties, the PAF constructed by the new PPG exhibits fast photoactivation and a low background signal, and the resulting fluorescence images display a signal-to-noise ratio greater than 780. It is anticipated that the superior photolysis performance makes the PPGs a novel platform for the construction of photo responsive systems in a variety of applications.