Abstract
The light-induced spin and structure changes upon excitation of the singlet metal-to-ligand charge transfer (1MLCT) state of Fe(II)-polypyridine complexes are investigated in detail in the case of aqueous iron(II)-tris-bipyridine ([FeII(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 1MLCT state from the singlet low-spin ground state (1GS) as the following sequence: 1,3MLCT → 5T → 1GS, 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 [FeII(bpy)3]2+ are of general validity to the entire family of Fe(II)-polypyridine complexes.
Original language | English |
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Pages (from-to) | 2677-2686 |
Number of pages | 9 |
Journal | Coordination Chemistry Reviews |
Volume | 254 |
Issue number | 21-22 |
DOIs | |
Publication status | Published - Nov 2010 |
Externally published | Yes |
Keywords
- Spin crossover; Pump–probe spectroscopy; Ultrafast; Optical absorptionX-ray absorption; Fluorescence up-conversion