Relaxation dynamics of transition-metal coordination complexes in solutions

Charge transfer usually competes with other photoinduced non-radiative loss channels, such as intersystem crossing, internal conversion, and parallel photochemical reactions. Therefore, revealing the relaxation mechanisms is a crucial point. Besides, the influence of the environment can also be decisive for the electron transfer dynamics in solid or soft-matter systems.

As a model system resembling the properties of more complex light-harvesting molecular compounds, we investigated the relaxation dynamics of ferricyanide dissolved in water [1]. We found that these dynamics involve fast and slow intersystem crossing, both occurring on a sub-picosecond timescale. Another study addressed the question of spin crossover mechanisms in iron tris-bipyridine [2]. The singlet-to-quintet spin transition was shown to involve both the direct and cascade channels. In linkage isomers, the relaxation dynamics can also involve structural changes. Such an effect was investigated in sodium nitroprusside [3]. The influence of the medium on the relaxation dynamics was investigated in ruthenium tris-bipyridine dissolved in ionic liquid [4]. The environment effect was fond to be small, presumably due to the large ligands of this molecular compound. This issue lies in the focus of our current studies.

References

[1] N. Engel,  S. I. Bokarev,  A. Moguilevski,  A. Raheem,  R. Al-Obaidi,  T. Möhle,  G. Grell,  K. R. Siefermann,  B. Abel,  S. Aziz,  O. Kühn,  M. Borgwardt,  I. Yu. Kiyan, E. F. Aziz, Light-induced relaxation dynamics in the ferricyanide ion revisited with ultrafast XUV photoelectron spectroscopy, Phys. Chem. Chem. Phys. 19, 14248 - 14255 (2017). DOI: 10.1039/c7cp01288h

[2] A. Moguilevski, M. Wilke, G. Grell, S. I. Bokarev, S. G. Aziz, N. Engel, A. A. Raheem, O. Kühn, I. Yu. Kiyan, E. F. Aziz, Ultrafast spin crossover in [FeII(bpy)3]2+: revealing two competing mechanisms by means of XUV photoemission spectroscopy, ChemPhysChem 18, 465 - 469 (2017). DOI: 10.1002/cphc.201601396

[3] A. A. Raheem, M. Wilke, M. Borgwardt, N. Engel, S. I. Bokarev, G. Grell, S. G. Aziz, O. Kühn, I. Yu. Kiyan, C. Merschjann, E. F. Aziz, Ultrafast kinetics of linkage isomerism in Na2[Fe(CN)5NO] aqueous solution revealed by time-resolved photoelectron spectroscopy, Structural Dynamics 4, 044031 (2017). DOI: 10.1063/1.4990567

[4] M. Borgwardt, M. Wilke, I. Yu. Kiyan, and E. F. Aziz, Ultrafast excited states dynamics of [Ru(bpy)3]2+ dissolved in ionic liquids, Phys. Chem. Chem. Phys. 18, 28893 - 28900 (2016). DOI: 10.1039/c6cp05655e