Influence of Alkoxy Groups on the Photoinduced Dynamics of Organic Molecules Exemplified on Alkyl Vinyl Ethers.

A series of different alkyl vinyl ethers is investigated to decipher the possible reaction channels upon photoexcitation to the π3s-Rydberg and the ππ*-valence state at 200 nm using time-resolved photoelectron spectroscopy and on-the-fly time-dependent density functional theory dynamics simulations. The results indicate two possible relaxation pathways: (1) a radiationless decay through the ππ*-state back to the ground state via torsion of the C═C double bond, in accordance with the dynamics found in ethylene; and (2) a fast dissociation of the C-O bond between the alkyl and the vinoxy group in the πσ*-state. The latter state can be accessed only after excitation to the π3s-Rydberg state (quantum yield of ∼50% according to the dynamics simulations). Additionally, the excited state barrier leading to formation of a vinyl radical was found to be too high to be crossed. These results indicate that the dynamics of ethers crucially depend on the excitation wavelength and that the πσ*-state constitutes an important competitive reaction channel that leads to dissociation of the molecules.