5-SFX (full name: 6-(Fluorescein-5-carboxamido)hexanoic acid, succinimidyl ester, single isomer) has a 6-atom aminohexanoyl spacer group that separates the fluorescein dye and the amine-reactive group. &lamba;Ex/&lamba; Em(pH9) = 494/521nm Yellow solid soluble in DMF, DMSO or pH>6.5 buffers Store at -20°C and protect from light C31H26N2O10 MW:586.55