Observing Optically Dark States in the Photoswitchable Azobenzene with Resonant Inelastic X-ray Scattering

Yin, Zhong; Odelius, Michael; Pietzsch, Annette; Foehlisch, Alexander; Ertan, Emelie; Rajkovic, Ivan; Banerjee, Ambar; Techert, Simone

doi:10.26434/chemrxiv-2025-x2hzr

Preprint

PUBDB-2025-05411

Observing Optically Dark States in the Photoswitchable Azobenzene with Resonant Inelastic X-ray Scattering

Yin, Z.Extern*XFEL.EU*DESY* ; Banerjee, A. (Corresponding author)Extern*XFEL.EU* ; Rajkovic, I.Extern* ; Ertan, E. ; Pietzsch, A.Extern*XFEL.EU* ; Foehlisch, A. (Corresponding author)Extern* ; Techert, S. (Corresponding author)XFEL.EU*DESY* ; Odelius, M. (Corresponding author)Extern*XFEL.EU*

2025

[10.26434/chemrxiv-2025-x2hzr]

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Please use a persistent id in citations: doi:10.26434/chemrxiv-2025-x2hzr doi:10.3204/PUBDB-2025-05411

Abstract: The trans-cis isomerization in azobenzene is a reversible reaction that has strong application potential ranging from photo-stimulating molecular motors to molecular electronics. Though azobenzene has been intensively and thoroughly investigated in optical spectroscopy, the S0 -> S1 transition is symmetry forbidden. Here, we report on measurements of resonant inelastic X-ray scattering (RIXS) at the nitrogen K-edge of the trans- and cis-forms of azobenzene dissolved in ethanol. In RIXS, we observe isomer-specific spectral features, which contain a distinct signature of the S1 state and further information on the electronic properties of the isomers of azobenzene. For the cis-isomer an additional peak arises, revealing a transition suppressed in the trans-conformation due to diferent orbital hybridization, thereby giving distinct spectral finn=gerprints to the trans- and cis-isomers of azobenzene in RIXS, containing information about valence excitations and their nitrogen character.

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