The photochemical ring-opening of 1,3-cyclohexadiene imaged by ultrafast electron diffraction

T J A Wolf; D M Sanchez; J Yang; R M Parrish; J P F Nunes; M Centurion; R Coffee; J P Cryan; M Gühr; K Hegazy; A Kirrander; R K Li; J Ruddock; X Shen; T Vecchione; S P Weathersby; P M Weber; K Wilkin; H Yong; Q Zheng; X J Wang; M P Minitti; T J Martínez

doi:10.1038/s41557-019-0252-7

The photochemical ring-opening of 1,3-cyclohexadiene imaged by ultrafast electron diffraction

Nat Chem. 2019 Jun;11(6):504-509. doi: 10.1038/s41557-019-0252-7. Epub 2019 Apr 15.

Authors

T J A Wolf¹, D M Sanchez^{2

3}, J Yang^{2

4}, R M Parrish^{2

3}, J P F Nunes^{5

6}, M Centurion⁶, R Coffee⁴, J P Cryan², M Gühr^{2

7}, K Hegazy^{2

8}, A Kirrander⁹, R K Li⁴, J Ruddock¹⁰, X Shen⁴, T Vecchione⁴, S P Weathersby⁴, P M Weber¹⁰, K Wilkin⁶, H Yong¹⁰, Q Zheng⁴, X J Wang¹¹, M P Minitti¹², T J Martínez^{13

14}

Affiliations

¹ Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA, USA. thomas.wolf@stanford.edu.
² Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
³ Department of Chemistry, Stanford University, Stanford, CA, USA.
⁴ SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
⁵ Department of Chemistry, University of York, York, UK.
⁶ Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, NE, USA.
⁷ Institut für Physik und Astronomie, Universität Potsdam, Potsdam, Germany.
⁸ Department of Physics, Stanford University, Stanford, CA, USA.
⁹ EaStCHEM, School of Chemistry, University of Edinburgh, Edinburgh, UK.
¹⁰ Department of Chemistry, Brown University, Providence, RI, USA.
¹¹ SLAC National Accelerator Laboratory, Menlo Park, CA, USA. wangxj@slac.stanford.edu.
¹² SLAC National Accelerator Laboratory, Menlo Park, CA, USA. minitti@slac.stanford.edu.
¹³ Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA, USA. todd.martinez@stanford.edu.
¹⁴ Department of Chemistry, Stanford University, Stanford, CA, USA. todd.martinez@stanford.edu.

PMID: 30988415
DOI: 10.1038/s41557-019-0252-7

Abstract

The ultrafast photoinduced ring-opening of 1,3-cyclohexadiene constitutes a textbook example of electrocyclic reactions in organic chemistry and a model for photobiological reactions in vitamin D synthesis. Although the relaxation from the photoexcited electronic state during the ring-opening has been investigated in numerous studies, the accompanying changes in atomic distance have not been resolved. Here we present a direct and unambiguous observation of the ring-opening reaction path on the femtosecond timescale and subångström length scale using megaelectronvolt ultrafast electron diffraction. We followed the carbon-carbon bond dissociation and the structural opening of the 1,3-cyclohexadiene ring by the direct measurement of time-dependent changes in the distribution of interatomic distances. We observed a substantial acceleration of the ring-opening motion after internal conversion to the ground state due to a steepening of the electronic potential gradient towards the product minima. The ring-opening motion transforms into rotation of the terminal ethylene groups in the photoproduct 1,3,5-hexatriene on the subpicosecond timescale.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.
Research Support, Non-U.S. Gov't