Activatable self-reporting cyclization reaction for in-cell synthesis of cyclocyanines

Generally, fluorescence "turn-on" click reactions require special activation triggers and heavily rely on preformed fluorophores. Herein, we reported an activatable self-reporting click-like reaction for one-pot synthesis of cyclic cyanines (CCClick) by clicking formaldehyde (FA) into dimeric Fischer bases, using biocompatible metal ions or complexes (e.g., copper, iron, and hemin) as an activator. CCClick involves FA-specific dehydration cyclization and metal-catalyzing oxidative dehydrogenation. Hemin-activated CCClick is flexible with Fischer base structures, satisfies the strict requirements for in-cell synthesis of bioimaging molecules and provides a convenient chemical tool for disease diagnosis.