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 S<sub>3</sub> state, which is populated for <i>hv</i> > 3.7 eV, is shown to decay predominantly by internal conversion to the S<sub>2</sub> state that in turn autodetaches to the neutral ground state. For <i>hv</i> > 4.1 eV, a new and favorable autodetachment channel from the S<sub>2</sub> 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.