Flipping fluorine chromophores: The unique fluorescence property of the chromophore from green fluorescent protein (GFP) of the jellyfish Aequorea victoria results from the rigid framework of its interactions with the surrounding protein matrix. The three-dimensional structure of 3-fluorotyrosine-containing "enhanced" GFP shows two conformational states of fluorine as an integral part of the chromophore in the crystalline state (see scheme). In this way, chromophore fluorination might be used as a tool to study its flipping and dynamics directly. This will certainly lead to enrichment or even a re-evaluation of the current concepts in this field.