Reactive dyes based on ruthenium complexes for use in fluorescence polarization assays and fluorescence lifetime imaging applications. 
This dye can be used to label carboxylic acids on biomolecules under mild conditions. Advantages of these dyes as protein labels include high photostability, good water solubility, a lack of dye-dye interactions and large Stokes′ shifts. In addition, the fluorescence signal of long-lived fluorophores can be gated to eliminate the emission from short-lifetime fluorophores and autofluorescence from cells and biomolecules to further improve sensitivity.