Excited State Dynamics of the Isolated Green Fluorescent Protein Chromophore Anion Following UV Excitation

A combined frequency-, angle-, and time-resolved photoelectron spectroscopy study is used to unravel the excited state dynamics following UV excitation of the isolated anionic chromophore of the green fluorescent protein (GFP). The optically bright S3 state, which is populated for hv > 3.7 eV, is shown to decay predominantly by internal conversion to the S2 state that in turn autodetaches to the neutral ground state. For hv > 4.1 eV, a new and favorable autodetachment channel from the S2 state becomes available, which leads to the formation of the neutral in an excited state. The results indicate that the UV excited state dynamics of the GFP chromophore involve a number of strongly coupled excited states.