UV Response of the Green Fluorescent Protein Chromophore: Insights from Ab Initio Nonadiabatic Simulations

state. Furthermore, the threshold energies of the shape and Feshbach resonances are very similar, with a low barrier separating these regions of the PES, leading to both states being populated and reversibly interconverting within 50 fs of the initial photoexcitation. As a result, rapid autoionization still precedes via the shape resonance. The picture that emerges thus reconciles the two competing views of the GFP chromophore's UV response: both internal conversion and IVR from the shape resonance state are operative. Our findings of the involvement of the Feshbach state suggest new strategies to engineer FP chromophores with tailored photostabilities.