Photo-induced primary processes of trans-[Co(acac)₂(N₃)(py)] in liquid solution studied by femtosecond vibrational and electronic spectroscopies

Abstract

The elementary light-triggered dynamics of the transition metal complex, trans-[Co^III(acac)₂(N₃)(py)] (trans-[1]), was investigated using femtosecond mid-infrared (mIR) and UV-Vis spectroscopies following ultrafast acetylacetonate-to-cobalt charge-transfer excitation at 266 nm. The spectro-temporal response is indicative of an ultrafast return to the electronic ground state via a sequential intramolecular electron transfer. The locally excited ligand-to-metal charge transfer state, ¹LMCT_acac, decays within 200 fs via azide-to-acac electron transfer to another charge-transfer state, ¹LMCT_azide, that features an azidyl radical ligand attached to a cobalt(II) center. A subsequent cobalt-to azidyl electron transfer occurring within 1.8 ps generates an excited metal centered state, ¹MC, thereby re-establishing the fully closed-shell character of the anionic azido and acac ligands. The fully relaxed electronic ground state of trans-[1] is then recovered via internal conversion and vibrational energy relaxation on a 10 ps-time scale.

GRAPHICAL ABSTRACT

KEYWORDS:

• Transition metal complexes
• photochemistry
• ultrafast spectroscopy

Acknowledgements

We thank Prof. Jürgen Troe for his inspirational abilities as a mentor and teacher of physical chemistry. We consider ourselves fortunate to be able to experience his contagious fascination for science and his boundless energy to advance knowledge.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the Priority Program SPP 2102 ‘Light-controlled reactivity of metal complexes’, grant VO-593/8-1 [project number 404522842].