Electron Density Analysis of the “O–O” Charge-Shift Bonding in Rubrene Endoperoxide

The Ambiguous Origin of Thermochromism in Molecular Crystals of Dichalcogenides: Chalcogen Bonds versus Dynamic Se-Se/Te-Te Bonds

We report thermochromism in crystals of diphenyl diselenide (dpdSe) and diphenyl ditelluride (dpdTe), which is at variance with the commonly known mechanisms of thermochromism in molecular crystals. Variable temperature neutron diffraction studies indicated no conformational change, tautomerization or phase transition between 100 K and 295 K. High-pressure crystallography studies indicated no associated piezochromism in dpdSe and dpdTe crystals. The evolution of the crystal structures and their electronic band structure with pressure and temperature reveal the contributions of intramolecular and intermolecular factors towards the origin of thermochromism-especially the intermolecular Se⋅⋅⋅Se and Te⋅⋅⋅Te chalcogen bonds and torsional modes of vibrations around the dynamic Se-Se and Te-Te bonds. Further, a co-crystal of dpdSe with iodine (dpdSe-I2 ) and an alloy crystal of dpdSe and dpdTe implied a predominantly intramolecular origin of the observed thermochromism associated with vibronic coupling.

Understanding and Controlling Fluorinated Diacyl Peroxides and Fluoroalkyl Radicals in Alkene Fluoroalkylations

The demand for practical methods for the synthesis of novel fluoroalkyl molecules is increasing owing to their diverse applications. Our group has achieved efficient difunctionalizing fluoroalkylations of alkenes using fluorinated carboxylic anhydrides as user-friendly fluoroalkyl sources. Fluorinated diacyl peroxide, prepared in situ from carboxylic anhydrides, enables the development of novel reactions when used as a radical fluoroalkylating reagent. In this account, we aim to provide an in-depth understanding of the structure, bonding, and reactivity of fluorinated diacyl peroxides and radicals as well as their control in fluoroalkylation reactions. In the first part of this account, the physical properties and reactivity of diacyl peroxides and fluoroalkyl radicals are described. In the subsequent part, we categorize the reactions into copper-catalyzed and metal-free methods utilizing the oxidizing properties of fluorinated diacyl peroxides. We also outline examples and mechanisms.

An atoms-in-molecules characterization of the nature of the OO bond in peroxides and nitroxide dimers

The quantum theory of atoms-in-molecules (QTAIM) method is used to examine the OO bond in peroxides (RO-OR) and nitroxide dimers (R₂ NO-ONR₂ ), including Fremy's salt. The electron density (ρ), electron kinetic energy density [K(ρ)], and Laplacian of the electron density (∇² ρ) at bond critical points characterize the nature of the OO bond. The data distinguish OO bonding of two kinds. Large values of ρ and positive ∇² ρ and K(ρ) suggest that simple peroxides have charge-shift bonds. Nitroxide dimers, with smaller ρ, positive ∇² ρ, and near-zero K(ρ), show a lack of shared electron density, suggesting there is no conventional OO bonding in these molecules. QTAIM analysis at the B3LYP/6-311+G(d,p) level of theory gives results in agreement with valence-bond theory and X-ray diffraction characterizations of peroxide OO bonds as charge-shift bonds. In contrast, CCSD/cc-pVDZ calculations fail to agree with previous results because of an insufficient, single-determinant treatment of the charge-shift bond.

Charge-Shift Bonding: A New and Unique Form of Bonding

Charge-shift bonds (CSBs) constitute a new class of bonds different than covalent/polar-covalent and ionic bonds. Bonding in CSBs does not arise from either the covalent or the ionic structures of the bond, but rather from the resonance interaction between the structures. This Essay describes the reasons why the CSB family was overlooked by valence-bond pioneers and then demonstrates that the unique status of CSBs is not theory-dependent. Thus, valence bond (VB), molecular orbital (MO), and energy decomposition analysis (EDA), as well as a variety of electron density theories all show the distinction of CSBs vis-à-vis covalent and ionic bonds. Furthermore, the covalent-ionic resonance energy can be quantified from experiment, and hence has the same essential status as resonance energies of organic molecules, e.g., benzene. The Essay ends by arguing that CSBs are a distinct family of bonding, with a potential to bring about a Renaissance in the mental map of the chemical bond, and to contribute to productive chemical diversity.

Firefly-like Water Splitting Cells Based on FRET Phenomena with Ultrahigh Performance over 12

A firefly-like chemiluminescence reaction was utilized in a ZrO₂ nanoparticle matrix of water splitting cells, where the chlorophyll of Lantana camara was used as the major photosensitizer to excite electrons to the conduction band of ZrO₂. The fluorescence resonance energy transfer (FRET) was induced by rubrene, a firefly-like chemiluminescence molecule, and Lantana camara chlorophyll combined with 9,10-diphenylanthracene. The ZrO₂ nanoparticle film coated by the chlorophyll of Lantana camara and 9,10-diphenylanthracene under chemiluminescence irradiation in 1 M KHCO₃ water solution demonstrated the highest photocurrent density (88.1 A/m²) and the highest water splitting efficiency (12.77%).