Femtosecond XANES Study of the Light-Induced Spin Crossover Dynamics in an Iron(II) Complex
X-ray absorption spectroscopy is a powerful probe of mol. structure, but it has previously been too slow to track the earliest dynamics after photoexcitation. We investigated the ultrafast formation of the lowest quintet state of aq. iron(II) tris(bipyridine) upon excitation of the singlet metal-to-ligand-charge-transfer (1MLCT) state by femtosecond optical pump/x-ray probe techniques based on x-ray absorption near-edge structure (XANES). By recording the intensity of a characteristic XANES feature as a function of laser pump/x-ray probe time delay, we find that the quintet state is populated in about 150 fs. The quintet state is further evidenced by its full XANES spectrum recorded at a 300-fs time delay. These results resolve a long-standing issue about the population mechanism of quintet states in iron(II)-based complexes, which we identify as a simple 1MLCT->3MLCT->5T cascade from the initially excited state. The time scale of the 3MLCT->5T relaxation corresponds to the period of the iron-nitrogen stretch vibration.
Keywords: Electron transfer; Energy level excitation; Excited state; Laser radiation; Molecular vibration; Photoexcitation; Singlet state (femtosecond XANES study of light-induced spin Crossover dynamics in Iron(II) complex); Ligands Role: PEP (Physical ; engineering or chemical process) ; PRP (Properties) ; PROC (Process) (femtosecond XANES study of light-induced spin Crossover dynamics in Iron(II) complex); Light; XANES spectra (femtosecond XANES study of light-induced spin crossover dynamics in iron(II) complex); Electronic state (quintet; femtosecond XANES study of light-induced spin Crossover dynamics in Iron(II) complex) ; femtosecond XANES light induced spin crossover dynamics iron complex
Optical, Electron, and Mass Spectroscopy and Other Related Properties
Laboratoire de Spectroscopie Ultrarapide, FSB-BSP, ISIC,Ecole Polytechnique Federale de Lausanne,Lausanne,Switz.
written in English.
Record created on 2006-02-27, modified on 2016-08-08