Hypoxia, generally considered as an oxygen concentration of <2%, is found in various diseases such as ischemia, 2,3 chronic kidney disease and cancer. Indeed, oxygen concentrations as low as around 1% may occur in ischemia and cancer, and selective in vivo visualization of such severe hypoxia is especially important for monitoring and understanding these diseases. To analyze hypoxia in cellulo and in vivo, various fluorescence probes have been developed. However, existing nearinfrared (NIR) small molecular probes that can be effectively used in vivo are also activated at oxygen concentrations around 5%. Therefore, there is a need for the development of NIR fluorescence probes able to selectively detect severe hypoxia as in vivo analytical and diagnostic tools.