Mapping the broadband circular dichroism of copolymer films with supramolecular chirality in time and space

Measurements of the electronic circular dichroism (CD) are highly sensitive to the absolute configuration and conformation of chiral molecules and supramolecular assemblies and have therefore found widespread application in the chemical and biological sciences. Here, we demonstrate an approach to simultaneously follow changes in the CD and absorption response of photoexcited systems over the ultraviolet−visible spectral range with 100 fs time resolution. We apply the concept to chiral polyfluorene copolymer thin films and track their electronic relaxation in detail. The transient CD signal stems from the supramolecular response of the system and provides information regarding the recovery of the electronic ground state. This allows for a quantification of singlet−singlet annihilation and charge-pair formation processes. Spatial mapping of chiral domains on femtosecond time scales with a resolution of 50 μm and diffraction-limited steady-state imaging of the circular dichroism and the circularly polarised luminescence (CPL) of the films is demonstrated.

A complete biomimetic iron-sulfur cubane redox series

Synthetic iron-sulfur cubanes are essential models for biological cofactors in the more complex enzymatic environments. However, a complete series of [Fe4S4]n complexes spanning all biorelevant oxidation states (n = 0-3+) has never been prepared. Here, we demonstrate that the use of a bulky arylthiolate ligand promoting the encapsulation of alkali-metal cations in the vicinity of the cubane enables the synthesis of such a series. Characterization by EPR, 57Fe Mössbauer spectroscopy, UV-Vis electronic absorption and variable-temperature X-ray diffraction analysis reveals key trends for the Fe4S4 core’s geometry as well as for the Mössbauer isomer shift, which both correlate systematically with oxidation state. Furthermore, we confirm the S=4 electronic ground state of the most reduced member, [Fe4S4]0, in agreement with that proposed for the all-ferrous cubanes in Nature.

A complete biomimetic iron-sulfur cubane redox series

Synthetic iron-sulfur cubanes are essential models for biological cofactors in the more complex enzymatic environments. However, a complete series of [Fe4S4]n complexes spanning all biorelevant oxidation states (n = 0-3+) has never been prepared. Here, we demonstrate that the use of a bulky arylthiolate ligand promoting the encapsulation of alkali-metal cations in the vicinity of the cubane enables the synthesis of such a series. Characterization by EPR, 57Fe Mössbauer spectroscopy, UV-Vis electronic absorption and variable-temperature X-ray diffraction analysis reveals key trends for the Fe4S4 core’s geometry as well as for the Mössbauer isomer shift, which both correlate systematically with oxidation state. Furthermore, we confirm the S=4 electronic ground state of the most reduced member, [Fe4S4]0, in agreement with that proposed for the all-ferrous cubanes in Nature.

A Computational Journey across Nitroxide Radicals: From Structure to Spectroscopic Properties and Beyond

Nitroxide radicals are characterized by a long-lived open-shell electronic ground state and are strongly sensitive to the chemical environment, thus representing ideal spin probes and spin labels for paramagnetic biomolecules and materials. However, the interpretation of spectroscopic parameters in structural and dynamic terms requires the aid of accurate quantum chemical computations. In this paper we validate a computational model rooted into double-hybrid functionals and second order vibrational perturbation theory. Then, we provide reference quantum chemical results for the structures, vibrational frequencies and other spectroscopic features of a large panel of nitroxides of current biological and/or technological interest.

A Comparative Study of Potential Energy Curves Analytical Representations for CO, N2, P2, and ScF in Their Ground Electronic States

In this study, a detailed comparative analysis of four different potential energy functions is elaborated. These potential energy functions namely are Morse, Deng-Fan, Varshni, and Lennard-Jones. Furthermore, a mathematical representation for long-range region is elucidated. As a study case, four diatomic molecules (CO, N2, P2, and ScF) in their electronic ground states were chosen. Subsequently, the corresponding dissociation energy as well as some spectroscopic parameters were calculated accordingly.

Mn-induced Fermi-surface reconstruction in the SmFeAsO parent compound

The electronic ground state of iron-based materials is unusually sensitive to electronic correlations. Among others, its delicate balance is profoundly affected by the insertion of magnetic impurities in the FeAs layers. Here, we address the effects of Fe-to-Mn substitution in the non-superconducting Sm-1111 pnictide parent compound via a comparative study of SmFe$$_{1-x}$$ 1 - x Mn$$_{x}$$ x AsO samples with $$x(\text{Mn})=$$ x ( Mn ) = 0.05 and 0.10. Magnetization, Hall effect, and muon-spin spectroscopy data provide a coherent picture, indicating a weakening of the commensurate Fe spin-density-wave (SDW) order, as shown by the lowering of the SDW transition temperature $$T_\text{SDW}$$ T SDW with increasing Mn content, and the unexpected appearance of another magnetic order, occurring at $$T^{*} \approx 10$$ T ∗ ≈ 10 and 20 K for $$x=0.05$$ x = 0.05 and 0.10, respectively. We attribute the new magnetic transition at $$T^{*}$$ T ∗ , occurring well inside the SDW phase, to a reorganization of the Fermi surface due to Fe-to-Mn substitutions. These give rise to enhanced magnetic fluctuations along the incommensurate wavevector $$\varvec{Q}_2 =(\pi \pm \delta ,\pi \pm \delta )$$ Q 2 = ( π ± δ , π ± δ ) , further increased by the RKKY interactions among Mn impurities.