A tetrazine-fused aggregation induced emission luminogen for bioorthogonal fluorogenic bioprobe

Bioorthogonal fluorogenic probes allow spatiotemporally controlled molecular bioimaging with minimal perturbation of the native cellular environment. Due to favorable kinetics and reaction specificity in a physiological environment, inverse electron-demand Diels - Alder reaction (iEDDA) for bioorthogonal fluorogenic bioimaging has gained immense attention in scientific field; however, the technique still needs to washout excess trans-cyclooctene labels, thereby reducing the robustness and experimental convenience. In the present study, we report tetrazine-modified aggregation-induced emission luminogens for bioorthogonal fluorogenic bioimaging. We found that a unique molecular design strategy allowed incorporation of tetrazine on aggregation-induced emission luminogens with excellent fluorogenic properties. Moreover, tetrazine modification of aggregationinduced emission luminogens results in non-radiative decay, which induces fluorescence quenching. The systematic tunability of the emission wavelength of the fluorescent core skeleton allowed successful development of three different colorful fluorogenic tetrazine-fluorophores. Furthermore, an aggregate formation study and computational calculations revealed a synergistic fluorescent quenching effect between intramolecular charge transfer and tetrazine-mediated non-radiative decay. The final simple conjugation between triphenylphosphonium and tetrazine-fluorophore enabled successful development of fluorogenic probes for spatiotemporally controlled bioorthogonal bioimaging of mitochondria in live cells with the iEDDA without washing the transcyclooctene label and tetrazine-fluorophore.