Tracking of azobenzene isomerization by X-ray emission spectroscopy

Cis-trans isomerizations are among the fundamental processes in photochemistry. In azobenzene or its derivatives this dynamics is, due to its reversibility, one of the reactions widely used in photostimulation of molecular motors or in molecular electronics. Though intensively investigated in the optical regime, no detailed study exists in the X-ray regime so far. Because the X-ray emission spectroscopy echoes the electronic structure sensitive to the geometry, this theoretical report based on the density functional theory and its time-dependent version presents different nitrogen K-edge X-ray emission spectra for cis and trans isomers with close interrelation to their electron configuration. Considering the spectrum along the isomerization path, these structural signatures can be utilized to probe the isomerization dynamics in the excited molecule. The scheme can further be generalized to the element specific photoreactions.