Photoactivated In Situ Generation of Near Infrared Cyanines for Spatiotemporally Controlled Fluorescence Imaging in Living Cells

Abstract Photoactivated trimerization of 2,3,3‐trimethyl‐3 H ‐indole derivatives created near infrared fluorophore Cy5. The synthetic method is air‐tolerant, photosensitizer free, metal free, and condensation agent free. Living cells make Cy5 on a time scale of minutes under white light irradiation at a low power intensity, with the monomer as the only exogenous agent. The new method is promising to find applications in cell studies for in situ spatiotemporally controlled fluorescence imaging in living cells.