Figure 3.

Energy profiles along the S₁ photoisomerization coordinate of 1. The structures (geometrical parameters in Å and degrees) document the progression of the molecular structure along the coordinate (see ref. 16). ■ show the CASPT2 S₁ energy profile, and □ show the CASSCF energy profile before PT2 correction. ● and ♦ show the CASPT2 S₂ and S₀ energy profiles along the same coordinate, respectively. Notice that, because of the S₁/S₀ curve crossing, at the 90° CI structure the state labeled S₀ is ca. 1 kcal⋅mol⁻¹ higher than that labeled S₁. For the sake of simplicity we maintain this inverted labeling throughout the paper.