Relationship between photoisomerization path and intersection space in a retinal chromophore model

Area of Science:

• Photochemistry
• Quantum Chemistry
• Molecular Dynamics

Background:

• Retinal chromophores are crucial in vision and light-sensitive proteins.
• Understanding excited-state dynamics is key to their function.
• Conical intersections are traditionally thought to dominate excited-state decay.

Purpose of the Study:

• To investigate the intersection space (IS) between ground and excited electronic states in a retinal chromophore model.
• To analyze the relationship between the IS and the excited-state isomerization pathway.
• To explore the role of IS in the decay to the ground state.

Main Methods:

• Utilized ab initio CASSCF (Complete Active Space Self-Consistent Field) computations.
• Mapped a low-lying segment of the intersection space (IS).
• Analyzed the structural and energetic proximity of the IS to the Z --> E isomerization path.

Main Results:

• The computed IS segment was found to be energetically and structurally close to the excited-state Z --> E isomerization path.
• The IS segment and isomerization path remained roughly parallel.
• The IS and isomerization path merged near 70 degrees of double bond twisting.

Conclusions:

• The findings support a model where extended segments of the intersection space contribute to ground-state decay.
• This challenges the notion that decay is solely governed by single conical intersections.
• Suggests a more nuanced understanding of excited-state dynamics in retinal chromophores is needed.