Time-Resolved Relaxation Studies of Spin Crossover Systems in Solution

Structural Determination of a Short-Lived Excited Iron(II) Complex by Picosecond X-Ray Absorption Spectroscopy

“…In order to extract the excited state structure correctly, f t must be known, and we measured a value of 22 2% at t 50 ps, in laser-only pumpprobe experiments carried out under identical experimental conditions (laser fluence, sample concentration, and thickness) as in the x-ray experiments. The fractional HS population was estimated from the bleach of the ground state absorption upon 400 nm excitation [8], taking into account the unit quantum yield for populating the quintet state [7]. The recovered HS state XAS spectrum is shown in Fig.…”

“…The population of the HS state of Fe(II)-based SCO complexes can be triggered optically in the so-called light-induced excited spin state trapping (LIESST) process [1,6]. However, the lifetime of the HS state of Fe II bpy 3 2 is limited to microseconds at cryogenic temperatures, in contrast to the light-induced HS state of SCO complexes with lowtemperature lifetimes of more than 10 h. Photoexcitation of Fe II bpy 3 2 by UV-visible light populates the singlet metal-to-ligand-charge-transfer ( 1 MLCT) states, and is followed by a cascade of intersystem crossing steps through MLCT and ligand-field (LF) states, which brings the system to its lowest-lying quintet state (HS), 5 T 2 , with almost unit quantum yield within <1 ps [7,8]. At room temperature, this state relaxes nonradiatively to the LS ground state in 0:6 ns in aqueous solutions.…”

Picosecond X-ray Absorption Spectroscopy of a Photoinduced Iron(II) Spin Crossover Reaction in Solution

“…These observations enabled the characterization of the kinetics associated with the photoinduced SCO event using femtosecond transient absorption spectroscopy and the results are summarized in Figure 1c. 11,37,38 Here we consider the structural changes associated with the ultrafast photoinduced conversion of the ground low-spin 1 A 1 state to the excited high-spin 5 T 2 state of [Fe(tren(py) 3 )](PF 6 ) 2 dissolved in acetonitrile solution using synchrotron-based XAS. Time-resolved X-ray absorption spectra of [Fe(tren(py) 3 )](PF 6 ) 2 are collected following excitation with a 100 fs optical pulse, and the results are compared with the steady-state X-ray absorption spectrum of its high-spin analogue, [Fe(tren(6-Mepy) 3 )](PF 6 ) 2 .…”

Density functional theory calculations and vibrational spectroscopy on iron spin-crossover compounds

“…The time dependence of the HS -LS relaxation has been studied between 10 K and 44 K by means of magnetic susceptibility measurements; the obtained vibrational frequencies fit well to the distribution of the vibrational frequencies used to simulate experimental HS-LS relaxation rates. While the time-dependent studies on [Fe(trim) 2 ]2Cl 2 have been performed at low temperatures and at time scales up to ~20 hours, the [Fe(btpa)] (PF 6 ) 2 complex (with an octadentate polypyridine ligand) and its hexacoordinated analogue [Fe(b(bdpa))](PF 6 ) 2 have been investigated by nanosecond time-resolved resonance Raman spectroscopy [48,49]. A biexponential relaxation of the HS state was found which confirms the existence of two isomerical HS states in [Fe(btpa)](PF 6 ) 2 with life times at room temperature of < 100 ns and < 2000 ns.…”