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