Transient photoelectrons and linkage isomerism

Linkage isomerism is a well-known phenomenon in coordination chemistry. Multiatomic ligands can bind to a central metal atom with either of their ends. In some compounds, ligands can undergo a change of their orientation upon absorption of light. This effect can be used to, e.g., store information and energy. The prominent example is nitroprusside anion [Fe(CN)5NO]2-, where NO+ moiety changes from Fe-NO orientation to a side-on one with both N and O bound to iron. In the recent work, we have applied both transient photoelectron spectroscopy and theoretical modeling to reveal the ultrafast kinetics of this process:

A.A. Raheem, M. Wilke, M. Borgwardt, N. Engel, S.I. Bokarev*, G. Grell, S.G. Aziz, O. Kühn, I.Yu. Kiyan, Ch. 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)

Nuclear vibrations in X-ray spectra with a fine-tooth comb

One might remember the post where I have written about nuclear correlation effects showing up in absorption and resonant inelastic X-ray scattering spectra. A few days ago we have published a follow-up article, where this effect is scrutinously dissected:

Sven Karsten,  Sergey I. Bokarev,  Saadullah G. Aziz,  Sergei D. Ivanov, Oliver Kühn A time-correlation function approach to nuclear dynamical effects in X-ray spectroscopy J. Chem. Phys. 146, 224203 (2017).

X-ray nuclear dynamics

In the article, you can find an explicit derivation of the time-domain working expressions, a detailed description of our protocol, loads of formulas and graphs – the whole nine yards. Fans of math should do appreciate Sven’s efforts. Even more important, it represents a critical view of the method and suggests the route how to improve the main pitfalls of classical approximation with moderate effort.

 

Photodynamics in ferricyanide revisited

In continuation of our collaboration with Prof. Emad F. Aziz and Dr. Igor Yu. Kiyan from Helmholtz-Zentrum in Berlin, a new investigation has been recently published. In this study, we address the early photodynamics of ferricyanide ion in solution applying transient XUV photoelectron spectroscopy in tandem with theoretical modeling.

Light-induced relaxation dynamics of the ferricyanide ion revisited by ultrafast XUV photoelectron spectroscopy Phys. Chem. Chem. Phys., 2017,19, 14248-14255

Get

This combination has been already applied by us to unravel peculiarities of spin crossover in [Fe(bpy)3]2+ complex. Here, we have addressed the problem of charge localization and symmetry-breaking in the simple prototypical coordination compound – ferricyanide. Upon absorption of UV light, it is excited to the charge-transfer state, which can undergo non-radiative relaxation to the ground state or be involved in further chemical reactions. This is a usual trait of coordination and organometallic compounds, which is often used by nature and chemists in, e.g., photosynthesis or photocatalytic retrieval of ecologic fuels.

In previous UV pump – IR probe spectroscopic study of the photochemical fate of ferricyanide, it was concluded that the initially populated charge-delocalized state relaxes to the localized one and the process is driven by the reorganization of the polar solvent. However, we obtained strong evidence for the spin crossover followed by geometrical distortions due to Jahn–Teller effect, rather than localization/delocalization dynamics, as suggested previously. Remarkably, our interpretation also consistently explains the transient features observed in UV-IR pump-probe experiments along with transient XUV PES.

More on spin state dynamics

Recently, I wrote about our ultrafast spin dynamics project. The first publication in Phys. Rev. Lett. was a proof of concept article where we have shown the possibility of soft X-ray light to trigger an unprecedentedly fast change of a spin state. A follow-up article presenting the theoretical method used in this investigation in detail also appeared recently in the issue of Molecular Physics devoted to the anniversary of Andre D. Bandrauk:

Huihui Wang, Sergey I. Bokarev, Saadullah G. Aziz, Oliver Kühn Density matrix-based time-dependent configuration interaction approach to ultrafast spin-flip dynamics Mol. Phys. (2017) 1-10.

In this article, we reformulate the problem in the form of a density matrix which allows one to treat general open quantum systems with energy dissipation. In addition to the more thorough study of the influence of different parameters of an excitation pulse on the dynamics, we also discuss a regime where the strong electron correlation plays a decisive role. It was shown that core-excited electronic states may demonstrate entangled dynamics both due to the strong spin-orbit coupling and electron correlation. This makes them interesting objects for the future studies of the ultimate limits of the ultrafast electron motion in atoms, molecules, and extended systems.

16th International Congress of Quantum Chemistry

It is time already to make plans for the next year. I have recently got the first info message from the 16th ICQC organizing committee. Next year it will be held in Menton, France. I have attended the previous congress in Beijing in 2015 and even won the best poster prize.

16_icqc_banner_small_1

There is only one session, what is convenient since one has an opportunity to attend all talks. However, this means that only invited talks are included into the program. Other participants are assumed to present posters. Because of this peculiarity, the poster sessions looked quite impressive. I have never seen such amount of eminent professors standing near their posters. It has been a nice opportunity to talk to some of them in an informal atmosphere. Summarizing, I can definitely recommend this event.

Photosensitizers for photocatalytic water splitting

I suppose that you have noticed the hype around new energy sources during last decades even if you are not working in this field. As a continuation of the Light2Hydrogen project, we have also addressed the properties of quite popular iridium-based photosensitizers – molecules which absorb light and transfer energy or electrons further to catalysts. The idea behind this project is to use sunlight to split water into hydrogen and oxygen. The former can be then used as an ecologically clean fuel since upon combustion it produces only water.

inorganics-05-00023-ag-550

In collaboration with the group of Stefan Lochbrunner, we have studied the influence of chemical derivation onto the absorption spectra as well as the nature of the most important electronic states.  The “bright” absorbing states are important to acquire as much solar energy as possible. For this purpose, it is of interest to shift them to lower energies to increase the overlap with the sun spectrum. In turn, the character of the lowest “dark” state is essential for the efficiency of further reactions, for instance, electron transfer to water reduction agents. We have looked at a series of organic ligands bound to iridium ions and formulated recommendations which can help for the rational design of the photocatalysts.

The article is published in a themed issue under the editorship of Matthias Bauer:

O.S. Bokareva, T. Möhle, A. Neubauer, S.I. Bokarev, S. Lochbrunner, O. Kühn Chemical Tuning and Absorption Properties of Iridium Photosensitizers for Photocatalytic  Applications Inorganics 2017, 5(2), 23.