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The selective formation of antimony‐carbon bonds via organic superbase catalysis under metal‐ and salt‐free conditions is reported. This novel approach utilizes electron‐deficient stibine, Sb(C6F5)3, to give upon base‐catalyzed reactions with weakly acidic aromatic and heteroaromatic hydrocarbons access to a range of new aromatic and heteroaromatic stibines, respectively, with loss of C6HF5. Also, the significantly less electron‐deficient stibines, Ph2SbC6F5 and PhSb(C6F5)2 smoothly underwent base‐catalyzed exchange reactions with a range of terminal alkynes to generate the stibines of formulae PhSb(C≡CPh)2, and Ph2SbC≡CR [R=C6H5, C6H4‐NO2, COOEt, CH2Cl, CH2NEt2, CH2OSiMe3, Sb(C6H5)2], respectively. These formal substitution reactions proceed with high selectivity as only the C6F5 groups serve as a leaving group to be liberated as C6HF5 upon formal proton transfer from the alkyne. Kinetic studies of the base‐catalyzed reaction of Ph2SbC6F5 with phenyl acetylene to form Ph2SbC≡CPh and C6HF5 suggested the empirical rate law to exhibit a first‐order dependence with respect to the base catalyst, alkyne and stibine. DFT calculations support a pathway proceeding via a concerted σ‐bond metathesis transition state, where the base catalyst activates the Sb‐C6F5 bond sequence through secondary bond interactions. [ABSTRACT FROM AUTHOR]

This work provides a detailed multi‐component analysis of aromaticity in monosubstituted (X = CH3, CH2−, CH2+, NH2, NH−, NH+, OH, O−, and O+) and para‐homodisubstituted (X = CH3, CH2, NH2, NH, OH, and O) benzene derivatives. We investigate the effects of substituents using single‐reference (B3LYP/DFT) and multireference (CASSCF/MRCI) methods, focusing on structural (HOMA), vibrational (AI(vib)), topological (ELFπ), electronic (MCI), magnetic (NICS), and stability (S0–T1 splitting) properties. The findings reveal that appropriate π‐electron‐donating and π‐electron‐accepting substituents with suitable size and symmetry can interact with the π‐system of the ring, significantly influencing π‐electron delocalization. While the charge factor has a minimal impact on π‐electron delocalization, the presence of a pz orbital capable of interacting with the π‐electron delocalization is the primary factor leading to a deviation from the typical aromaticity characteristics observed in benzene. [ABSTRACT FROM AUTHOR]

Cation‐π interactions are theoretically investigated for alkali metal cation (M+)‐circumcoronene (CC) complexes (M = Li, Na, K), in gas phase and in aqueous solution with consideration of micro‐ and global solvation models using the DFT/PBEh‐3c‐RI/TZVP method. The solvent effect on the M+–CC energy interaction regarding the cation size and the stability of inner‐ and outer‐sphere [M(H2O)n]+–CC complexes are calculated by means of geometry optimizations and potential energy (PE) curves. The PE curves, calculated as a function of perpendicular distance of M+ to the CC plane, predicted one energy minimum for each of the isolated M+–CC complexes. However, for microhydrated complexes, two minima assigned to two different surface complexations were obtained. Microhydrated Li+ and Na+ favored outer‐sphere complexation while inner‐sphere complexation was found more stable for microhydrated K+. These results illustrate nicely the key role, which the cation radius plays for the polarization of the water molecules and the aromatic system. [ABSTRACT FROM AUTHOR]

Time‐dependent density functional theory (TDDFT) was applied to gain insights into the electronic and vibrational spectroscopic properties of an important electron transport mediator, methyl viologen (MV2+). An organic dication, MV2+ has numerous applications in electrochemistry that include energy conversion and storage, environmental remediation, and chemical sensing and electrosynthesis. MV2+ is easily reduced by a single electron transfer to form a radical cation species (MV•+), which has an intense UV–visible absorption near 600 nm. The redox properties of the MV2+/MV•+ couple and light‐sensitivity of MV•+ have made the system appealing for photo‐electrochemical energy conversion (e.g., solar hydrogen generation from water) and the study of photo‐induced charge transfer processes through electronic absorption and resonance Raman spectroscopic measurements. The reported work applies leading TDDFT approaches to investigate the electronic and vibrational spectroscopic properties of MV2+ and MV•+. Using a conventional hybrid exchange functional (B3‐LYP) and a long‐range corrected hybrid exchange functional (ωB97X‐D3), including with a conductor‐like polarizable continuum model to account for solvation, the electronic absorption and resonance Raman spectra predicted are in good agreement with experiment. Also analyzed are the charge transfer character and natural transition orbitals derived from the TDDFT vertical excitations calculated. The findings and models developed further the understanding of the electronic properties of viologens and related organic redox mediators important in renewable energy applications and serve as a reference for guiding the interpretation of electronic absorption and Raman spectra of the ions. [ABSTRACT FROM AUTHOR]

The alternant polycyclic aromatic hydrocarbon pyrene has photophysical properties that can be tuned with different donor and acceptor substituents. Recently, a D (donor)‐Pyrene (bridge)‐A (acceptor) system, DPA, with the electron donor N,N‐dimethylaniline (DMA), and the electron acceptor trifluoromethylphenyl (TFM), was investigated by means of time‐resolved spectroscopic measurements (J. Phys. Chem. Lett. 2021, 12, 2226–2231). DPA shows great promise for potential applications in organic electronic devices. In this work, we used the ab initio second‐order algebraic diagrammatic construction method ADC(2) to investigate the excited‐state properties of a series of analogous DPA systems, including the originally synthesized DPAs. The additionally investigated substituents were amino, fluorine, and methoxy as donors and nitrile and nitro groups as acceptors. The focus of this work was on characterizing the lowest excited singlet states regarding charge transfer (CT) and local excitation (LE) characters. For the DMA‐pyrene‐TFM system, the ADC(2) calculations show two initial electronic states relevant for interpreting the photodynamics. The bright S1 state is locally excited within the pyrene moiety, and an S2 state is localized ~0.5 eV above S1 and characterized as a donor to pyrene CT state. HOMO and LUMO energies were employed to assess the efficiency of the DPA compounds for organic photovoltaics (OPVs). HOMO‐LUMO and optical gaps were used to estimate power conversion and light‐harvesting efficiencies for practical applications in organic solar cells. Considering the systems using smaller D/A substituents, compounds with the strong acceptor NO2 substituent group show enhanced CT and promising properties for use in OPVs. Some of the other compounds with small substituents are also found to be competitive in this regard. [ABSTRACT FROM AUTHOR]

The kinetics of a strategically synthesized burn rate enhancer (BRE) are investigated in its reaction with ammonium perchlorate (AP). The BRE is designed for multifunctionality by 1) producing reactive gases that couple with AP gas production; 2) trapping reactive gases with high surface area; and 3) exposing metal cations to incite exothermic reactions at a temperature coincident with AP decomposition. This study advances inorganic synthesis by introducing a metal inorganic framework (MIF) composed of an aluminum cation (Al+3) surrounded by inorganic "linker" molecules of oxidizing species. To increase surface area, a porous, amorphous MIF (a‐MIF) is synthesized by controlling solution properties of an acid–base precipitation reaction. Upon gas generation, high surface area and aluminum‐rich surface of a‐MIF accelerate AP decomposition and induce an exothermic reaction that is otherwise endothermic in thermal equilibrium analysis. AP decomposition rate is advanced by reducing peak onset temperature and increasing decomposition rate with addition of a‐MIF (i.e., from 17% min−1 at 401 °C to 18% min−1 at 365 °C). Enthalpy of AP decomposition increases from +240 J g−1 to −1040 J g−1. Results introduce an approach for increasing the decomposition rate of solid oxidizers by demonstrating a recipe for designing and synthesizing an MIF. [ABSTRACT FROM AUTHOR]

The chemical stability and the low‐lying singlet and triplet excited states of BN‐n‐acenes (n = 1–7) were studied using single reference and multireference methodologies. From the calculations, descriptors such as the singlet‐triplet splitting, the natural orbital (NO) occupations and aromaticity indexes are used to provide structural and energetic analysis. The boron and nitrogen atoms form an isoelectronic pair of two carbon atoms, which was used for the complete substitution of these units in the acene series. The structural analysis confirms the effects originated from the insertion of a uniform pattern of electronegativity difference within the molecular systems. The covalent bonds tend to be strongly polarized which does not happen in the case of a carbon‐only framework. This effect leads to a charge transfer between neighbor atoms resulting in a more strengthened structure, keeping the aromaticity roughly constant along the chain. The singlet‐triplet splitting also agrees with this stability trend, maintaining a consistent gap value for all molecules. The BN‐n‐acenes molecules possess a ground state with monoconfigurational character indicating their electronic stability. The low‐lying singlet excited states have charge transfer character, which proceeds from nitrogen to boron. [ABSTRACT FROM AUTHOR]

Humic substances (HSs) as a major part of soil organic matter (SOM) are complex combinations of natural organic matter, which are ubiquitous in the environment and occur predominantly in soils, residues and natural water. They play a crucial role in the fate and behaviour of contaminants in the environment. In this work, an HS nanopore model was based on a structural motif containing polar and nonpolar domains. The polar domain was represented by the carboxyl groups that predominate in the composition of HSs, whereas the nonpolar domain was constructed by aliphatic chains. The effect of hydrophobic/hydrophilic interactions on sorption in HSs was analysed by the inclusion of the nonpolar polycyclic aromatic hydrocarbon naphthalene and the polar herbicide 2‐methyl‐4‐chlorophenoxyacetic acid (MCPA) in the nanopore. Water cluster was also included to allow the formation of the water molecular bridges (WaMB), which stabilized the whole system. Thermodynamic potential‐of‐mean‐force (PMF) calculations by means of classical molecular dynamics simulations were performed to investigate the effect of polar and nonpolar domains in the adsorption mechanism. The polar MCPA molecule was stabilized at the hydrophilic water–HS interface, whereas nonpolar naphthalene was stabilized inside of the hydrophobic nanovoid of the HS nanopore model. The obtained results demonstrated that the adsorption strength of HSs regarding polar and nonpolar species is similar, but the adsorption mechanisms differ. Highlights: The work elucidates the adsorption mechanism of polar and nonpolar species in SOM at the molecular scale.The derived HS model was suitable to describe and explain the adsorption properties of SOM by means of constrained molecular dynamics simulations.Adsorption mechanisms for polar and nonpolar species in SOM differ. Polar molecules prefer the water–SOM interface, whereas nonpolar molecules are trapped in hydrophobic nanovoids of SOM.Molecular dynamics simulation is an effective method providing a detailed description of the adsorption processes in SOM. [ABSTRACT FROM AUTHOR]

Theoretical descriptions of excited state proton transfer (ESPT) have had various degrees of success. This work presents a theoretical description of the photodissociation of the 7‐hydroxyflavylium cation (7‐HF), the fundamental chromophoric moiety of anthocyanin natural plant pigments. ESPT of 7‐HF is promoted by a significant shift of charge away from the OH group in the first singlet excited state, leading smoothly to the excited conjugate base and a protonated water cluster. Several factors contribute to the consistency of the results of the present study: (1) the theoretical approach (TD‐DFT with the B3‐LYP functional and def2‐TZVP basis set utilizing Grimme's D3 dispersion correction); (2) the modeling of the solvent effect combining hydrogen bonding of the photoacid to a cluster of discrete water molecules in a water‐like continuum solvent (COSMO); (3) the large S1‐S2 energy gap of flavylium cations; and (4) the electrostatics of the ESPT in which a proton is transferred from a cationic photoacid to water without Coulombic interaction between the proton and the conjugate base. [ABSTRACT FROM AUTHOR]

Semiclassical ab initio simulations of the absorption spectra of neutral and anionic p-hydroxybenzylidene-2,3-dimethylimidazolinone ( p- HBDI), a model chromophore of green fluorescent protein ( GFP) and of a positively charged neutral (N+)- HBDI chromophore model, were performed in gas phase with the resolution-of-identity algebraic diagrammatic construction through second-order ( RI- ADC(2)) method. The calculated absorption spectra in gas phase are composed of one band centered at 3.51 eV ( HBDI), 2.50 eV ( HBDI−) and 3.02 eV ((N+)- HBDI) owing to the absorption of the first 1 ππ* transition. Band maxima are redshifted by ~0.1 eV with respect to the corresponding vertical energies. The COSMO- RI- ADC(2) calculations of the first vertical excitation energy of HBDI, HBDI− and (N+)- HBDI forms in polar solution including microsolvation simulate the observed solvent redshift for neutral HBDI and the solvent blueshift of the HBDI− and (N+)- HBDI forms. The state-specific solvation approach applied to TDDFT calculations reproduced the experimental solvent shifts for the three HBDI forms, demonstrating a more accurate theoretical description as compared to the linear-response TDDFT approach. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of the fluorene-pyridine copolymer (FPy)n, (n = 1–4) were investigated theoretically by means of quantum mechanical calculations based on density functional theory (DFT) and time-dependent DFT (TD-DFT) using the B3LYP functional. Geometry optimizations of these oligomers were performed for the ground state and the lowest excited state. It was found that (FPy)n is nonplanar in its ground state, whereas a more pronounced trend toward planarity is observed in the S1 state. Absorption and fluorescence energies have been extrapolated to infinite chain length making use of their good linearity with respect to 1/n. An extrapolated value of 2.64 eV is obtained for vertical excitation energy. The S1←S0 electronic excitation is characterized as a highest occupied molecular orbital to lowest unoccupied molecular orbital transition and is dominating in terms of oscillator strength. Fluorescence energies and radiative lifetime were calculated as well. The obtained results indicate that the fluorescence energy and radiative lifetime of (FPy)n are 2.16 eV and 0.38 ns, respectively. The decrease of fluorescence energy and radiative lifetime with the increase in the chain length is discussed. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [ABSTRACT FROM AUTHOR]