We report on an element-selective study of the fate of charge carriers in photoexcited inorganic CsPbBr3 and CsPb(ClBr)3 perovskite nanocrystals in toluene solutions using time-resolved X-ray absorption spectroscopy with 80 ps time resolution. Probing the Br K-edge, the Pb L3-edge, and the Cs L2-edge, we find that holes in the valence band are localized at Br atoms, forming small polarons, while electrons appear as delocalized in the conduction band. No signature of either electronic or structural changes is observed at the Cs L2-edge. The results at the Br and Pb edges suggest the existence of a weakly localized exciton, while the absence of signatures at the Cs edge indicates that the Cs+ cation plays no role in the charge transport, at least beyond 80 ps. This first, time-resolved element-specific study of perovskites helps understand the rather modest charge carrier mobilities in these materials.

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A new redox couple, [Cu(bpye)2]+/2+, has been synthesized and applied in DSSCs. Overall efficiencies above 9.0% and good photostability were obtained. Excellent electrolyte charge transport, fast regeneration and low recombination are the major reasons for the high efficiencies.

The development of next-generation perovskitebased optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equilibrium conditions. While it has become increasingly evident for CsPbBr 3 perovskites that the Pb−Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work, we demonstrate that the photoinduced lattice changes in the system are due to a specific polaronic distortion, associated with the activation of a longitudinal optical phonon mode at 18 meV by electron−phonon coupling, and we quantify the associated structural changes with atomic-level precision. Key to this achievement is the combination of timeresolved and temperature-dependent studies at Br K and Pb L 3 X-ray absorption edges with refined ab initio simulations, which fully account for the screened core-hole final state effects on the X-ray absorption spectra. From the temporal kinetics, we show that carrier recombination reversibly unlocks the structural deformation at both Br and Pb sites. The comparison with the temperaturedependent XAS results rules out thermal effects as the primary source of distortion of the Pb−Br bonding motif during photoexcitation. Our work provides a comprehensive description of the CsPbBr 3 perovskites' photophysics, offering novel insights on the light-induced response of the system and its exceptional optoelectronic properties.

The structure–function relationship is at the heart of biology, and major protein deformations are correlated to specific functions. For ferrous heme proteins, doming is associated with the respiratory function in hemoglobin and myoglobins. Cytochrome c (Cyt c) has evolved to become an important electron-transfer protein in humans. In its ferrous form, it undergoes ligand release and doming upon photoexcitation, but its ferric form does not release the distal ligand, while the return to the ground state has been attributed to thermal relaxation. Here, by combining femtosecond Fe Kα and Kβ X-ray emission spectroscopy (XES) with Fe K-edge X-ray absorption near-edge structure (XANES), we demonstrate that the photocycle of ferric Cyt c is entirely due to a cascade among excited spin states of the iron ion, causing the ferric heme to undergo doming, which we identify. We also argue that this pattern is common to a wide diversity of ferric heme proteins, raising the question of the biological relevance of doming in such proteins.

A number of paramagnetic silylated d1 group 4 metallates were prepared by reaction of potassium tris(trimethylsilyl)silanide with group 4 metallates of the type K[Cp2MCl2] (M = Ti, Zr, Hf). The outcomes of the reactions differ for all three metals. While for the hafnium case the expected complex [Cp2Hf{Si(SiMe3)3}2]− was obtained, the analogous titanium reaction led to a product with two Si(H)(SiMe3)2 ligands. The reaction with zirconium caused the formation of a dinuclear fulvalene bridged complex. The desired [Cp2Zr{Si(SiMe3)3}2]− could be obtained by reduction of Cp2Zr{Si(SiMe3)3}2 with potassium. In related reactions of potassium tris(trimethylsilyl)silanide with some lanthanidocenes Cp3Ln (Ln = Ce, Sm, Gd, Ho, Tm) complexes of the type [Cp3Ln Si(SiMe3)3]− with either [18-crown-6·K]+ or the complex ion [18-crown-6·K·Cp·K·18-crown-6] as counterions were obtained. Due to d1 or fn electron configuration, unambiguous characterization of all obtained complexes could only be achieved by single crystal XRD diffraction analysis.

In haemoglobin the change from the low-spin (LS) hexacoordinated haem to the high spin (HS, S = 2) pentacoordinated domed deoxy-myoglobin (deoxyMb) form upon ligand detachment from the haem and the reverse process upon ligand binding are what ultimately drives the respiratory function. Here we probe them in the case of Myoglobin-NO (MbNO) using element-and spin-sensitive femtosecond Fe K α and K β X-ray emission spectroscopy at an X-ray free-electron laser (FEL). We find that the change from the LS (S = 1/2) MbNO to the HS haem occurs in~800 fs, and that it proceeds via an intermediate (S = 1) spin state. We also show that upon NO recombination, the return to the planar MbNO ground state is an electronic relaxation from HS to LS taking place in~30 ps. Thus, the entire ligand dissociation-recombination cycle in MbNO is a spin cross-over followed by a reverse spin cross-over process.

Most chemical and biochemical reactions in nature and in industrial processes are driven by thermal effects that bring the reactants above the energy barrier for reaction. In aqueous solutions, this process can also be triggered by the laser driven temperature jump (T-jump) method, in which the water vibrational (stretch, bend, or combination) modes are excited by a short laser pulse, leading to a temperature increase in the irradiated volume within a few picoseconds. The combination of the laser T-jump with X-ray spectroscopic probes would add element-specificity as well as sensitivity to the structure, the oxidation state, and the spin state of the intermediates of reactions. Here, we present preliminary results of a near infrared pump/X-ray absorption spectroscopy probe to study the ligand exchange of an octahedral aqueous Cobalt complex, which is known to pass through intermediate steps yielding tetrahedral chlorinated as final species. The structural changes of the chemical reaction are monitored with great sensitivity, even in the presence of a mild local increase in temperature. This work opens perspectives for the study of non-light-driven reactions using time-resolved X-ray spectroscopic methods.