Theoretical Study of the Photoisomerization Mechanism of All-Trans-Retinyl Acetate
Kochman Michal Andrzej, Palczewski Krzysztof, Kubas Adam
JOURNAL OF PHYSICAL CHEMISTRY A, 2021
The compound 9-cis-retinyl acetate (9-cis-RAc) is a precursor to 9-cisretinal, which has potential application in the treatment of some hereditary diseases of the retina. An attractive synthetic route to 9-cis-RAc is based on the photoisomerization reaction of the readily available all-trans-RAc. In the present study, we examine the mechanism of the photoisomerization reaction with the use of state-of-the-art electronic structure calculations for two polyenic model compounds: tEtEt-octatetraene and tEtEtEc-2,6-dimethyl-1,3,5,7,9-decapentaene. The occurrence of photoisomerization is attributed to a chain-kinking mechanism, whereby a series of S-1/S-0 conical intersections associated with kinking deformations at different positions along the polyenic chain mediate internal conversion to the S-0 state, and subsequent isomerization around one of the double bonds. Two other possible photoisomerization mechanisms are taken into account, but they are rejected as incompatible with simulation results and/or the available spectroscopic data.