The o- and p-amino green-fluorescence-protein synthetic chromophores (GFPSCs) were synthesized from the corresponding o- and p-nitro protecting group. Among the four protecting groups of the o-amino group, the o-nitro protecting group is the only choice to synthesize the o-amino GFPSCs. The first singlet excited states of o- and p-amino GFPSCs carry significant charge-transfer character through the mechanism of photoinduced charge transfer (PCT). The o-amino GFPSCs can serve as wavelength-ratiometric fluorescence sensors that selectively recognize Cr(3+) in aqueous medium through a PCT mechanism.