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"Pseudo-Bimolecular [2+2] Cycloaddition Studied by Time-Resolved
Photoelectron Spectroscopy" Rasmus Y. Brogaard, Andrey E. Boguslavskiy, Oliver Schalk, Gary D. Enright, Henning Hopf, Vitaly A. Raev, Peter G. Jones, Ditte L. Thomsen, Theis I. Sølling, Albert StolowChemistry - A European Journal, 17, 3922 (2011). Abstract: The first study of pseudo-bimolecular cycloaddition reaction dynamics in the gas phase is presented. We used femtosecond time-resolved photoelectron spectroscopy (TRPES) to study the [2+2] photocycloaddition in the model system pseudo-gemdivinyl[2.2]paracyclophane. From X-ray crystal diffraction measurements we found that the ground-state molecule can exist in two conformers; a reactive one in which the vinyl groups are immediately situated for [2+2] cycloaddition and a nonreactive conformer in which they point in opposite directions. From the measured S1 lifetimes we assigned a clear relation between the conformation and the excited- state reactivity; the reactive conformer has a lifetime of 13 ps, populating the ground state through a conical intersection leading to [2+2] cycloaddition, whereas the nonreactive conformer has a lifetime of 400 ps. Ab initio calculations were performed to locate the relevant conical intersection (CI) and calculate an excited-state [2+2] cycloaddition reaction path. The interpretation of the results is supported by experimental results on the similar but nonreactive pseudo-paradivinyl[2.2]paracyclophane, which has a lifetime of more than 500 ps in the S1 state. This publication has not been written at BMO BMO authors (in alphabetic order): Oliver Schalk  WWW-Version |