Photochemically Induced 1,3-Butadiene Ring-Closure from the Topological Analysis of the Electron Localization Function Viewpoint.

The electronic rearrangement featuring the photochemically-induced 1,3-cis-butadiene is discussed within a bonding evolution theory (BET) perspective based on the topological analysis of the electron localization function and Thom's catastrophe theory. The process involves the vertical singlet-singlet excitation S 0 →S 2 , and the subsequent deactivation implying the S 2 /S 1 and S 1 /S 0 conical intersection regions. BET results reveal that the new CC bond is finally formed on the S 0 surface, as also recently found in the photochemical addition of two ethylenes [Phys. Chem. Chem. Phys. 23, 20598, (2021)].