The thiol reactive Oregon Green® 488 iodoacetamide can be used to can be used to create green fluorescent bioconjugates with excitation/emission maxima ~496/524 nm.
This fluorinated analog of fluorescein overcomes some of the key limitations of fluorescein, including greater photostability and a lower pK_a (pK_a ~ 4.7 versus 6.4 for fluorescein), making its fluorescence essentially pH insensitive in the physiological pH range.