Cy3B (Figure 1) is the least fluorescent dye belonging to the cyanine family of synthetic polymethine dyes and is a conformationally blocked isomer of the Cy3 dye. As such, it does not undergo photoisomerization events and is characterized by high stability and a high degree of fluorescence emission. Like Cy3, Cy3B is most commonly paired with the dark quencher BHQ-2.
Figure 1. Structure of 5'-Cyanine 3B (R = sequence).
metabion offers the Cy3B modification in its DNA portfolio: