Solvatochromism of the Green Fluorescence Protein Chromophore and Its Derivatives

The solvatochromic behavior of the green fluorescence protein (GFP) chromophore (p-hydroxybenzylideneimidazolone, p-HBDI) and its derivatives (p-methoxybenzylideneimidazolone, p-MeOBDI, and N-methyl-p-hydroxybenzylideneimidazolonium iodide, p-HBDIMe+) was studied using UV−vis−absorption spectroscopy in a wide array of solvents. The relative contribution of specific (polarity) vs nonspecific (hydrogen-bonding) solvation to the absorbance spectra was studied. On the basis of these data, we discuss the nature of the absorption peak of the protonated and deprotonated forms of the wild-type GFP.