Synthetic Green Fluorescent Protein Chromophores

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.