Highly fluorogenic tetrazine bioorthogonal probes emitting at near-infrared wavelengths are in strong demand for biomedical imaging applications . Herein, we have developed a strategy for forming a palette of novel``Huaxi-Fluor"probes in situ, whose fluorescence increases hundreds of times upon forming of the bioorthogonal reaction product, pyridazine . The resulting probes show large Stokes shifts and high quantum yields . Manipulating the conjugate length and pull-push strength in the fluorophore skeleton allows the emission wavelength to be fine-tuned from 556 to 728 nm . The highly photo-stable and biocompatible probes are suitable for visualizing organelles in live cells without a washing step and for imaging of tumors in live small animals to depths of 500 µm by two-photon excitation.