Alexa Fluor® 647 conjugates are highly photostable and remain fluorescent over a broad pH range. The excitation and emission maxima are nearly identical to those of APC. However, APC tends to be brighter while Alexa Fluor® 647 is more optimal for intracellular applications. This fluorochrome exhibits uncommon photostability, making it an ideal choice for use in fluorescence microscopy. Due to nearly identical excitation and emission properties but different spillover characteristics, APC and Alexa Fluor® 647 cannot be used simultaneously.