Pseudo-bimolecular [2+2] cycloaddition studied by time-resolved photoelectron spectroscopy

TY - JOUR

T1 - Pseudo-bimolecular [2+2] cycloaddition studied by time-resolved photoelectron spectroscopy

AU - Brogaard, Rasmus Y

AU - Boguslavskiy, Andrey E

AU - Schalk, Oliver

AU - Enright, Gary D

AU - Hopf, Henning

AU - Raev, Vitaly A

AU - Jones, Peter G

AU - Thomsen, Ditte L

AU - Sølling, Theis I

AU - Stolow, Albert

N1 - Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

PY - 2011/3/28

Y1 - 2011/3/28

N2 - 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-gem-divinyl[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 S(1) 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-para-divinyl[2.2]paracyclophane, which has a lifetime of more than 500 ps in the S(1) state.

AB - 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-gem-divinyl[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 S(1) 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-para-divinyl[2.2]paracyclophane, which has a lifetime of more than 500 ps in the S(1) state.

U2 - 10.1002/chem.201002928

DO - 10.1002/chem.201002928

M3 - Journal article

C2 - 21365700

SN - 0947-6539

VL - 17

SP - 3922

EP - 3931

JO - Chemistry: A European Journal

JF - Chemistry: A European Journal

IS - 14

ER -