Synthesis, Photophysical Properties, and Application of <i>o</i>- and <i>p</i>‑Amino Green Fluorescence Protein Synthetic Chromophores

The <i>o</i>- and <i>p</i>-amino green-fluorescence-protein synthetic chromophores (GFPSCs) were synthesized from the corresponding <i>o</i>- and <i>p</i>-nitro protecting group. Among the four protecting groups of the <i>o</i>-amino group, the <i>o</i>-nitro protecting group is the only choice to synthesize the <i>o</i>-amino GFPSCs. The first singlet excited states of <i>o</i>- and <i>p</i>-amino GFPSCs carry significant charge-transfer character through the mechanism of photoinduced charge transfer (PCT). The <i>o</i>-amino GFPSCs can serve as wavelength-ratiometric fluorescence sensors that selectively recognize Cr³⁺ in aqueous medium through a PCT mechanism