Tetramethyrhodamine is a synthetic fluorescent compound. Dissolved in methanol, it has a maximum absorbance 541 nm, and maximum emission at 567 nm. It's chemical formula is C25H21N3O3S. Tetramethyrhodamine (TMR) is used in may biological applications to label proteins, nucleotides, organelles, and cells. It's bright pink. Don't spill it on you, because it stains, and it's carcinogenic.