iFluor® 405 azide is reasonably stable and shows good reactivity and selectivity with the alkyne group in click chemistry. iFluor® dyes are optimized for labeling proteins, in particular, antibodies. These dyes are bright, photostable, and have minimal quenching on proteins. They can be well excited by the major laser lines of fluorescence instruments (e.g., 350, 405, 488, 555, and 633 nm). iFluor® 405 dyes have fluorescence excitation and emission maxima of ~403 nm and ~427 nm respectively. The iFluor® 405 family has spectral properties essentially identical to those of Alexa Fluor® 405 (Alexa Fluor® 405 is the trademark of ThermoFisher). Its fluorescence is pH-independent from pH 3 to 11. These spectral characteristics make this new dye family a great alternative to Alexa Fluor® 405.