Cyanine5 is an extremely popular fluorophore. This dye emits in red region. It has an outstanding extinction coefficient, and a good fluorescence quantum yield, and is therefore very bright. It is very photostable; its ability to blink in the presence of thiols makes it a dye of choice for STORM super-resolution microscopy. The dye is extensively used in qPCR. It forms a FRET pair with Cyanine3 as donor.
A sulfonated, water soluble version sulfo-Cyanine5 is also available.