Ultrafast Nonadiabatic Dynamics of [FeII(bpy)3]2+ in Solution
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- 作者：Wojciech Gawelda ; Andrea Cannizzo ; Van-Thai Pham ; Frank van Mourik ; Christian Bressler ; Majed Chergui
- 刊名：Journal of the American Chemical Society
- 出版年：2007
- 出版时间：July 4, 2007
- 年：2007
- 卷：129
- 期：26
- 页码：8199 - 8206
- 全文大小：349K
- 年卷期：v.129,no.26(July 4, 2007)
- ISSN：1520-5126
文摘
The ultrafast relaxation of aqueous iron(II)-tris(bipyridine) upon excitation into the singlet metal-to-ligand charge-transfer band (1MLCT) has been characterized by femtosecond fluorescence up-conversionand transient absorption (TA) studies. The fluorescence experiment shows a very short-lived broad 1MLCTemission band at ~600 nm, which decays in 
20 fs, and a weak emission at ~660 nm, which we attributeto the 3MLCT, populated by intersystem crossing (ISC) from the 1MLCT state. The TA studies show ashort-lived (<150 fs) excited-state absorption (ESA) below 400 nm, and a longer-lived one above 550 nm,along with the ground-state bleach (GSB). We identify the short-lived ESA as being due to the 3MLCTstate. The long-lived ESA decay and the GSB recovery occur on the time scale of the lowest excited high-spin quintet state 5T2 lifetime. A singular value decomposition and a global analysis of the TA data, basedon a sequential relaxation model, reveal three characteristic time scales: 120 fs, 960 fs, and 665 ps. Thefirst is the decay of the 3MLCT, the second is identified as the population time of the 5T2 state, while thethird is its decay time to the ground state. The anomalously high ISC rate is identical in [RuII(bpy)3]2+ andis therefore independent of the spin-orbit constant of the metal atom. To reconcile these rates with theregular quasi-harmonic vibrational progression of the 1MLCT absorption, we propose a simple model ofavoided crossings between singlet and triplet potential curves, induced by the strong spin-orbit interaction.The subsequent relaxation steps down to the 5T2 state dissipate ~2000 cm-1/100 fs. This rate is discussed,and we conclude that it nevertheless can be described by the Fermi golden rule, despite its high value.
20 fs, and a weak emission at ~660 nm, which we attributeto the 3MLCT, populated by intersystem crossing (ISC) from the 1MLCT state. The TA studies show ashort-lived (<150 fs) excited-state absorption (ESA) below 400 nm, and a longer-lived one above 550 nm,along with the ground-state bleach (GSB). We identify the short-lived ESA as being due to the 3MLCTstate. The long-lived ESA decay and the GSB recovery occur on the time scale of the lowest excited high-spin quintet state 5T2 lifetime. A singular value decomposition and a global analysis of the TA data, basedon a sequential relaxation model, reveal three characteristic time scales: 120 fs, 960 fs, and 665 ps. Thefirst is the decay of the 3MLCT, the second is identified as the population time of the 5T2 state, while thethird is its decay time to the ground state. The anomalously high ISC rate is identical in [RuII(bpy)3]2+ andis therefore independent of the spin-orbit constant of the metal atom. To reconcile these rates with theregular quasi-harmonic vibrational progression of the 1MLCT absorption, we propose a simple model ofavoided crossings between singlet and triplet potential curves, induced by the strong spin-orbit interaction.The subsequent relaxation steps down to the 5T2 state dissipate ~2000 cm-1/100 fs. This rate is discussed,and we conclude that it nevertheless can be described by the Fermi golden rule, despite its high value.