Rhodamine

[1] Aside from their major applications, they are often used as a tracer dye, e.g. to determine the rate and direction of flow and transport of water.

TRITC is the base rhodamine molecule functionalized with an isothiocyanate group (−N=C=S), replacing a hydrogen atom on the bottom ring of the structure.

A succinimidyl-ester functional group attached to the rhodamine core, creating NHS-rhodamine, forms another common amine-reactive derivative.

Other derivatives of rhodamine include newer fluorophores such as Alexa 546, Alexa 633, DyLight 550 and DyLight 633, HiLyte fluor 555 HiLyte 594, Janelia Dyes JF549 and JF669 have been tailored for various chemical and biological applications where higher photostability, increased brightness, different spectral characteristics, or different attachment groups are needed.

Specifically designed substituents also allows xanthenes to bear specific functions activatable upon excitation by visible light, e.g. they could act as photoremovable protecting group for carboxylates and halides,[7] carbon monoxide (thus being a photoCORM),[8] or added as a secondary functionality of fluorescent dyes, e.g. fluorescent pH indicators.