TY - JOUR
T1 - Light-induced spin crossover in Fe(II)-based complexes: The full photocycle unraveled by ultrafast optical and X-ray spectroscopies
AU - Cannizzo, A.
AU - Milne, C.J.
AU - Consani, C.
AU - Gawelda, W.
AU - Bressler, C.
AU - van Mourik, F.
AU - Chergui, M.
PY - 2010/11
Y1 - 2010/11
N2 - 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.
AB - 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.
KW - Spin crossover; Pump–probe spectroscopy; Ultrafast; Optical absorptionX-ray absorption; Fluorescence up-conversion
UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77956231370&partnerID=MN8TOARS
U2 - 10.1016/j.ccr.2009.12.007
DO - 10.1016/j.ccr.2009.12.007
M3 - Article
VL - 254
SP - 2677
EP - 2686
JO - Coordination Chemistry Reviews
JF - Coordination Chemistry Reviews
IS - 21-22
ER -