Stepwise Activated Coupling Reaction and Its Potentional Application in Targeting Bio-probes Preparation

Fluorescent probes, as an important tool for biological research, has attracted more and more attention, and the coupling of fluorescent units with targeted components is the key technology. Reported previously fluorescent modification to the targeted components usually underwent preliminary post-modification of fluorophores with unique groups such as carboxyl, azide, alkynyl et al, and then fast coupling with targeted structures via the typical click reaction or biorthogonal chemistry, but need complex chemical synthesis and head-scratching purification. Here, an innovative strategy was developed based on stepwise activated coupling modification. A series of donor-acceptor (D-A) typed probe frameworks were constructed after introducing different commercial electronic donors to the electron-withdrawing squaric acid core. Intriguingly, these D-A-typed light-emitting frameworks were further activated by the visual light to obtain different 3,4-diarylmaleic anhydride (MAH) precursors of bioconjugation reaction due to novel light triggered ring enlargement effect. Importantly, these MAH-precursors could trigger catalyst-free coupling reaction with primary amine group of organic small molecules and biological macromolecules at ambient temperature, achieving the effective combination between different fluorescent precursors and abundant targeted components. This strategy was expected to have great application potentiality on biological imaging and theranostic mechanism.