"The Patern`o-Büchi Reaction: Importance of Triplet States in The
Excited-State Reaction Pathway"Rasmus Y. Brogaard, Oliver Schalk, Andrey E. Boguslavskiy, Gary D. Enright, Henning Hopf, Vitaly Raev, Eliza Tarcoveanu, Theis I. Sølling, and Albert Stolow
Phys. Chem. Chem. Phys. 14, 8572 - 8580 (2012).
The Patern`o-B¨uchi (PB) reaction between an excited carbonyl compound and an alkene has been widely studied, but so far little
is known about the excited-state dynamics of the reaction. In this work we use a model compound in which a formyl and a
vinyl group are attached to a [2.2]paracyclophane in order to place the units in pre-reactive position for the PB reaction. We
study the excited-state dynamics of the isolated molecules in a molecular beam using femtosecond time-resolved photoelectron
spectroscopy and ab initio calculations. The results show that fast inter-system crossing of within two picoseconds competes
efficiently with the reaction in the singlet manifold. Thus, the PB reaction in this model system takes place in the triplet state on
a time scale of nanoseconds. This result stresses the importance of triplet states in the excited-state pathway of the PB reaction
involving aromatic carbonyl compounds, even in situations in which the reaction partners are in immediate vicinity.
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