The gas-phase absorption properties of a blue GFP-mutant chromophore have been investigated in an electrostatic heavy-ion storage ring combined with an electrospray ion source. From the production of neutral photofragments, the gas-phase absorption profiles of both protonated and deprotonated forms have been obtained and compared with their homologues in the liquid phase and in the protein. Maximum absorption for the anion is found around 456 nm in solution and in the gas phase. It matches one absorption maximum in the W7 protein, which suggests that this is due to an anionic form of the chromophore-similar to the case of the GFP. For the W7 chromophore cation, the gas-phase absorption band exhibits a doublet feature in the gas-phase with maxima at 454 and 477 nm. Solvation effects are more pronounced for the cation than for the anion and the observed shifts in the absorption maxima may be explained by charge delocalization. (C) 2003 American Institute of Physics.