Figure 5. Ultra-fast internal conversion mechanism of the trans anion.

(A) Snapshot at the conical intersection: the chromophore is twisted around torsion B, yet the hydrogen bonded network in the chromophore cavity remains intact. (B) Ground (S₀, black) and excited (S₁, red) potential energy traces along the QM/MM molecular dynamics trajectory. Photon absorption (green arrow) brings the chromophore into S₁ (yellow area) until it decays back to S₀ at the conical intersection seam (dashed line). (C) Time-evolution of the torsion angles A (magenta) and B (blue). (D) S₀ and S₁ energies along a representative excited state trajectory of A_trans. The protein environment strongly stabilizes S₀ and S₁ (black and red lines, respectively) relative to the gas phase (dashed blue and green lines, respectively). The energy offset is 1.9686×10⁶ kJ/mol. (E) Energy difference ΔE between the protein and the gas phase for S₀ (black) and S₁ (red).