Fig. 3.

Computed MEPs along the central C4═C5 S₁ photoisomerization coordinate (A) (for comparison, the corresponding path in vacuo is also reported; see dotted lines) (6), and C2═C3 S₁ photoisomerization coordinate (B) of 1. Energy profiles have been scaled to match CASPT2 energies. The structures (geometrical parameters in Å and degrees) document the progression of the molecular structure along the coordinate. FC₁ is the Franck-Condon structure, SP₁ corresponds to the covalent-like S₁ skeletal relaxed species, CI₁ and TM₁ are the TICT (≈90° twisted) S₁/S₀ CI funnel and twisted minimum, respectively, and TS1₁ and TS2₁ are the transition states located along the paths. Ionic- and covalent-like S₁ surfaces (as resulting from the analysis of the CAS-SCF wave functions) are illustrated by a white and gray background, respectively. The bar diagrams give the S₀ (black), S₁ (light gray), and S₂ (dark gray) CAS-SCF/6-31G^* Mulliken charges for the twisting left and right moieties (the dotted line represents the border between the two moieties) of 1 along the illustrated photoisomerization paths.