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Abstract The optimization of the quantum efficiency of single-molecule light-driven rotary motors typically relies on chemical modifications. While, in isolated conditions, computational methods have been frequently used to design more efficient motors, the role played by the solvent environment has not been satisfactorily investigated. In this study, we used multiscale nonadiabatic molecular dynamics simulations of the working cycle of a 2-stroke photon-only molecular rotary motor. The results, which display dynamics consistent with the available transient spectroscopy measurements, predict a considerable decrease in the isomerisation quantum efficiency in methanol solution with respect to the gas phase. The origin of such a decrease is traced back to the ability of the motor to establish hydrogen bonds with solvent molecules. The analysis suggests that a modified motor with a reduced ability to form hydrogen bonds will display increased quantum efficiency, therefore extending the set of engineering rules available for designing light-driven rotary motors. 

An exploration of group twoansa-metallocenes for solvent effects, interannular bridges, and quantitative bond strength through local mode analysis. 

Abstract ContextThe efficient extraction of uranyl from spent nuclear fuel wastewater for subsequent reprocessing and reuse is an essential effort toward minimization of long-lived radioactive waste. N-substituted amides and Schiff base ligands are propitious candidates, where extraction occurs via complexation with the uranyl moiety. In this study, we extensively probed chemical bonding in various uranyl complexes, utilizing the local vibrational modes theory alongside QTAIM and NBO analyses. We focused on (i) the assessment of the equatorial O-U and N-U bonding, including the question of chelation, and (ii) how the strength of the axial U$$=$$ $=$ O bonds of the uranyl moiety changes upon complexation. Our results reveal that the strength of the equatorial uranium-ligand interactions correlates with their covalent character and with charge donation from O and N lone pairs into the vacant uranium orbitals. We also found an inverse relationship between the covalent character of the equatorial ligand bonds and the strength of the axial uranium-oxygen bond. In summary, our study provides valuable data for a strategic modulation of N-substituted amide and Schiff base ligands towards the maximization of uranyl extraction. MethodQuantum chemistry calculations were performed under the PBE0 level of theory, paired with the relativistic NESCau Hamiltonian, currently implemented in Cologne2020 (interfaced with Gaussian16). Wave functions were expanded in the cc-pwCVTZ-X2C basis set for uranium and Dunning’s cc-pVTZ for the remaining atoms. For the bonding properties, we utilized the package LModeA in the local modes analyses, AIMALL in the QTAIM calculations, and NBO 7.0 for the NBO analyses. Graphical abstract 

Abstract The photophysical properties of a series of recently synthesized single benzene fluorophores were investigated using ensemble density functional theory calculations. The energetic stability of the ground and excited state species were counterposed against the aromaticity index derived from local vibrational modes. It was found that the large Stokes shift of the fluorophores (up toca.5800 cm) originates from the effect of electron donating and electron withdrawing substituents rather than ‐delocalization and related (anti‐)aromaticity. On the basis of nonadiabatic molecular dynamics simulations, the absence of fluorescence from one of the regioisomers was explained by the occurrence of easily accessible S/S conical intersections below the vertical excitation energy level. It is demonstrated in the manuscript that the analysis of local mode force constants and the related aromaticity index represent a useful tool for the characterization of ‐delocalization effects in ‐conjugated compounds. 

ABSTRACT Using the QM/MM methodology and a local mode analysis, we investigated a character and a strength of FeS bonds of heme groups in oxidized and reduced forms of Bacterioferritin fromAzotobacter vinelandii. The strength of the FeS bonds was correlated with a bond length, an energy density at a bond critical point, and a charge difference of the F and S atoms. Changing the oxidation state from ferrous to ferric generally makes the FeS bonds weaker, longer, more covalent, and more polar. We also investigated the SFeS bond bending and found that the stronger FeS bond, generally makes the SFeS bond bending stiffer, which could play a key role in the balance between ferric and ferrous oxidation states and related biological activities.