Photoactivatable Fluorogens by Intramolecular C-H Insertion of Perfluoroaryl Azide

Molecules capable of fluorescence turn-on by light are highly sought-after in spatio-temporal labeling, surface patterning, monitoring cellular and molecular events, and high-resolution fluorescence imaging. In this work, we report a fluorescence turn-on system based on photo-initiated intramolecular insertion of azide into the neighboring aromatic ring. The azide-masked fluorogens were efficiently synthesized via a cascade nucleophilic aromatic substitution of perfluoroaryl azides with carbazoles. The scaffold also allows for derivatization with biological ligands, as exemplified with D-mannose in this study. This photo-initiated intramolecular transformation led to high yields, high photo-conversion efficiency, and well-separated wavelengths for photo-activation and fluorescence excitation. The mannose-derivatized structure enabled spatio-temporal activation, and showed high contrast and signal amplification. Live cell imaging suggested that the mannose-tagged fluorogen was transported to the lysosomes.