Light-induced spin crossover in Fe(II)-based complexes: The full photocycle unraveled by ultrafast optical and X-ray spectroscopies
✍ Scribed by A. Cannizzo; C.J. Milne; C. Consani; W. Gawelda; Ch. Bressler; F. van Mourik; M. Chergui
- Publisher
- Elsevier Science
- Year
- 2010
- Tongue
- English
- Weight
- 794 KB
- Volume
- 254
- Category
- Article
- ISSN
- 0010-8545
No coin nor oath required. For personal study only.
✦ Synopsis
The light-induced spin and structure changes upon excitation of the singlet metal-to-ligand charge transfer ( 1 MLCT) state of Fe(II)-polypyridine complexes are investigated in detail in the case of aqueous iron(II)-tris-bipyridine ([Fe II (bpy) 3 ] 2+ ) by a combination of ultrafast optical and X-ray spectroscopies. Polychromatic femtosecond fluorescence up-conversion, transient absorption studies in the 290-600 nm region and femtosecond X-ray absorption spectroscopy allow us to retrieve the entire photocycle upon excitation of the 1 MLCT state from the singlet low-spin ground state ( 1 GS) as the following sequence: 1,3 MLCT → 5 T → 1 GS, which does not involve intermediate singlet and triplet ligand-field states. The population time of the HS state is found to be ∼150 fs, leaving it in a vibrationally hot state that relaxes in 2-3 ps, before decaying to the ground state in 650 ps. We also determine the structure of the high-spin quintet excited state by picosecond X-ray absorption spectroscopy at the K-edge of Fe. We argue that given the many common electronic (ordering of electronic states) and structural (Fe-N bond elongation in the high-spin state, Fe-N mode frequencies, etc.) similarities between all Fe(II)-polypyridine complexes, the results on the electronic relaxation processes reported in the case of [Fe II (bpy) 3 ] 2+ are of general validity to the entire family of Fe(II)-polypyridine complexes.