Ultrafast inter-ionic charge transfer of transition-metal complexes mapped by femtosecond X-ray powder diffraction

Abstract

The transient electronic and molecular structure arising from photoinduced charge transfer in transition metal complexes is studied by X-ray powder diffraction with a 100 fs temporal and atomic spatial resolution. Crystals containing a dense array of Fe(II)-tris(bipyridine) ([Fe(bpy)3](2 +)) complexes and their [Formula: see text] counterions display pronounced changes of electron density that occur within the first 100 fs after two-photon excitation of a small fraction of the [Fe(bpy)3](2 +) complexes. Transient electron density maps derived from the diffraction data reveal a transfer of electronic charge from the Fe atoms and-so far unknown-from the [Formula: see text] counterions to the bipyridine units. Such charge transfer (CT) is connected with changes of the inter-ionic and the Fe-bipyridine distances. An analysis of the electron density maps demonstrates the many-body character of charge transfer which affects approximately 30 complexes around a directly photoexcited one. The many-body behavior is governed by the long-range Coulomb forces in the ionic crystals and described by the concept of electronic polarons.

Fitting coupled potential energy surfaces for large systems: Method and construction of a 3-state representation for phenol photodissociation in the full 33 internal degrees of freedom using multireference configuration interaction determined data

“…Such transients show that the bpy ligands accept all charge transferred, with the major part coming from the counterions. The charge transfer shows a step-like time dependence which is in agreement with all-optical pumpprobe studies of the crystallites 59 and with the sub-150 fs formation kinetics of the 5 T state in solution. The long-range inter-ionic Coulomb interaction in the densely packed crystal is at the origin of the observed behavior.…”

“…25 is again mediated by the inner-ionic Coulomb interaction and has been analyzed in terms of electronic polaron formation in this prototype ionic material. 59 It should be noted that most applications of transition metal complexes require solid state materials for which the observed behavior is characteristic.…”

“…52 Up to 40 reflections have been detected simultaneously with the powder diffraction method for polycrystalline samples, [53][54][55][56][57][58][59] implemented with laser-driven plasma sources. Powder diffraction patterns consist of many Debye-Scherrer rings originating from crystallites in the powder with a random orientation of the reciprocal lattice vector G hkl .…”

Photoinduced Structural Dynamics of Molecular Systems Mapped by Time-Resolved X-ray Methods

“…291 This ultrafast structural dynamic in SCO solids was also investigated by x-ray diffraction by Chergui, Elsaesser and co-workers. 292 They used a laser-plasma source X-ray source delivering (Cu Kα, λ = 0.154 nm, 100 fs pulse duration)…”

Multidimensional scattering of attosecond x-ray pulses detected by photon-coincidence

“…We have developed a quantum-field treatment of x-ray scattering [15]. Extending that analysis to a molecule initially prepared in an electronic superposition state [16][17][18][19] will make it possible to track the time-dependent electron density.…”