5-CR110-PEO4 SE (full name: 5-Carboxyrhodamine 110-PEO4-propionate, succinimidyl ester, single isomer) is an excellent green fluorescent rhodamine dye for labeling amines. The dye has better solubility than the parent dye 5-CR110 SE and its long PEG spacer should reduce any steric effect of the dye on the molecule to be labeled.