Synthetic Green Fluorescent Protein Chromophores

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GFP is widely used as a biological marker because of its superb fluorescence properties. We have synthesized GFP chromophore and its derivatives, and their photochemistry and photophysics were investigated using various steady-state and time-resolved techniques. We first compared their optical properties between solution and solid state. We found some O-alkyl GFP chromophore derivatives exhibit large fluorescent enhancement in the solid state. Cis/trans isomerization is thought to be responsible for blinking behavior in fluorescent protein, however, the mechanism of the thermal reverse isomerization is more problematic. Using Hammett plot studies, we conceived, for the first time, a novel nucleophilic addition/elimination mechanism. Finally, a hydroxyl substituent at the meta position shows enhanced charge transfer and greater acidity in the excited state. As a result, we have demonstrated that the fast quenching of the excited state by internal conversion to the ground state is much slower in meta- than in para-HOBDI derivatives. This allows studies of this ultrafast intermolecular ESPT that competes with isomerization.