Competing ultrafast cis-trans isomerization and ring closure of cyclohepta-1,3-diene and cyclo-octa-1,3-diene

Abstract

Photochemically, s-cis-dienes can undergo cis-trans isomerization or electrocyclic ring closure to cyclobutenes. Modern quantum chemistry predicts that both reactions can originate from the same conical intersection and explains thereby why photochemical ring opening of cyclobutenes to dienes is often not stereospecific, although ring closure of dienes is. Evidence is found that the reaction path already branches earlier, investigating two cyclic dienes which were excited by a femtosecond UV pulse in the gas phase and probed by photoionization at 810 nm. The multistep path is assigned to the excited-state surfaces and ring closure of the ground-state trans isomers is also detected.

Acknowledgement

This work was supported by the Deutsche Forschungsgemeinschaft (project FU 363/1).