Figure 4. Influence of the protein environment on the photoisomerization process of the neutral asFP595 chromophore.

(A, C) Ground and excited state energies along trans-to-cis (A) and cis-to-trans (C) isomerization trajectories (run b, Table 1 and run a, Table 2). The protein environment stabilizes S₀ and S₁ (black and red lines, respectively) relative to the gas phase (dashed blue and green lines, respectively). (B, D) Energy difference between the protein and the gas phase. ΔE(S₀) = E(S₀, protein)−E(S₀, gas phase) is plotted in black, ΔE(S₁) = E(S₁, protein)−E(S₁, gas phase) in red. The protein environment energetically stabilizes S₁ more strongly than S₀. The vertical dashed black line represents the surface crossing. The energy offset in (A) and (C) is 1.9699×10⁶ kJ/mol.