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Nuclear magnetic resonance (NMR) chemical shifts and the magnetically induced current density (MICD) susceptibility of four osmium containing molecules have been calculated at the density functional theory (DFT) level using three relativistic levels of theory. The calculations were performed at the quasi-relativistic level using an effective core potential (ECP) for Os, at the all-electron scalar exact two-component (X2C) relativistic level, and at the relativistic X2C level including spin–orbit coupling (SO-X2C). In earlier studies, the osmapentalene (1) and the osmapentalynes (2 and 3) were considered Craig-type Möbius aromatic and it was suggested that the analogous osmium compound (4) is Craig-type Möbius antiaromatic. Here, the ring-current strengths were obtained with the gauge including magnetically induced currents (GIMIC) method by integrating the MICD susceptibility passing through planes that intersect chemical bonds and by line integration of the induced magnetic field using Ampεave;re-Maxwell's law. The ring-current calculations suggest that 1, 2 and 3 are weakly aromatic and that 4 is nonaromatic. The accuracy of the MICD susceptibility was assessed by comparing calculated NMR chemical shifts to available experimental data. Visualization of the MICD susceptibility shows that the ring current does not pass from one side of the molecular plane to the other, which means that the MICD susceptibility of the studied molecules does not exhibit any Möbius topology as one would expect for Craig-type Möbius aromatic and for Craig-type Möbius antiaromatic molecules. Thus, molecules 1–3 are not Craig-type Möbius aromatic and molecule 4 is not Craig-type Möbius antiaromatic as previously suggested. Calculations of the 1H NMR and 13C NMR chemical shifts of atoms near the Os atom show the importance of including spin–orbit effects. Overall, our study revisits the understanding of the aromaticity of organometallic molecules containing transition metals. [ABSTRACT FROM AUTHOR]

We have calculated the magnetically induced current density susceptibility for gold-containing organometallic molecular rings using the gauge-including magnetically induced currents (GIMIC) method. The aromatic nature has been determined by calculating the strength of the magnetically induced ring current susceptibility, which is often called ring current. To our knowledge, we show here for the first time that gold-containing organometallic rings may be aromatic or antiaromatic sustaining ring currents in the presence of an external magnetic field. The calculated aromatic character of the rings agrees with the aromatic nature one expects when using Hückel's aromaticity rules. The studied auracycles and diauracycles with 4n electrons in the conjugated orbitals generally sustain a weak paratropic ring current, whereas those having 4n + 2 electrons in the conjugated orbitals sustain a diatropic ring current that is almost as strong as that of benzene. The number of electrons are obtained by assuming that each C, N and Au atom of the ring contribute one electron, and a H atom connected to a N atom in the ring increases the number of electrons by one. An electron-attracting ligand at Au removes one electron from the ring. Formation of a short Au–Au bonding diauracycles reduces the number of electrons in the ring by two. [ABSTRACT FROM AUTHOR]

A theoretical model is proposed that allows the estimation of the quantum yield of phosphorescence of dye molecules in the vicinity of plasmonic nanoparticles. For this purpose, the rate constants of the radiative and nonradiative intramolecular transitions for rhodamine 123 (Rh123) and brominated rhodamine (Rh123-2Br) dyes have been calculated. The plasmon effect of Ag nanoparticles on various types of luminescence processes has been studied both theoretically and experimentally. We show that in the presence of a plasmonic nanoparticle, the efficiency of the immediate and delayed fluorescence increases significantly. The phosphorescence rate of the rhodamine dyes also increases near plasmonic nanoparticles. The long-lived luminescence i.e., delayed fluorescence and phosphorescence is more enhanced for Rh123-2Br than for Rh123. The largest phosphorescence quantum yield is obtained when the dye molecule is at a distance of 4–6 nm from the nanoparticle surface. Our results can be used in the design of plasmon-enhancing nanostructures for light-emitting media, organic light-emitting diodes, photovoltaic devices, and catalysts for activation of molecular oxygen. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) shielding constants have been calculated for Ni(II) bis(pentafluorophenyl)norcorrole and its face-to-face stacked dimer at the Hartree–Fock (HF), second-order Møller–Plesset perturbation theory (MP2), complete-active-space self-consistent-field (CASSCF) levels as well as at density functional theory (DFT) levels using several functionals. The calculated 1H NMR shielding constants agree rather well with the experimental ones. The shielding constants of N and Ni calculated at DFT, HF, and MP2 levels differ from those obtained in the CASSCF calculations due to near-degeneracy effects at the Ni atom. The calculated magnetically induced current densities show that the monomer is antiaromatic, sustaining a strong global paratropic ring current, and the dimer is aromatic, sustaining a strong diatropic ring current. Qualitatively the same current density is obtained at the employed levels of theory. The most accurate ring-current strengths are probably obtained at the MP2 level. The aromatic dimer has a short intermolecular distance of less than 3 Å. The intermolecular interaction changes the nature of the frontier orbitals leading to a formal double bond between the norcorrole macrocycles. [ABSTRACT FROM AUTHOR]

The effect of localized surface plasmon resonance (LSPR) of a system consisting of a highly dipolar merocyanine dye and a silver nanoparticle (NP) was studied experimentally and theoretically. A theoretical model for estimating the fluorescence quantum yield (ϕfl) using quantum chemical calculations of intramolecular and intermolecular electronic transition rate constants was developed. Calculations show that the main deactivation channels of the lowest excited singlet state of the studied merocyanines are internal conversion (kIC(S1 → S0)) and fluorescence (kr(S1 → S0)). The intersystem-crossing transition has a low probability due to the large energy difference between the singlet and triplet levels. In the presence of plasmonic NPs, the fluorescence quantum yield is increased by a factor of two according to both experiment and computations. The calculated values of ϕfl, when considering changes in kr(S1 → S0) and the energy-transfer rate constant (ktransfer) from the dye to the NP was also twice as large at distances of 6–8 nm between the NP and the dye molecule. We also found that the LSPR effect can be increased or decreased depending on the value of the dielectric constant (εm) of the environment. [ABSTRACT FROM AUTHOR]

The magnetically induced current–density susceptibility (MICD) of the [12]infinitene dianion and the induced magnetic field around it have been calculated at the density functional theory level. Separation of the MICD into diatropic and paratropic contributions shows that the MICD is dominated by the diatropic contribution in contrast to the notion that it is antiaromatic, which was reported in a recently published article. The MICD of the [12]infinitene dianion exhibits several through-space MICD pathways, whereas it sustains only weak local paratropic current-density contributions. We identified four main current-density pathways of which two are similar to the ones for neutral [12]infinitene. It is difficult to judge from calculations of the nucleus independent shielding constants and the induced magnetic field around the [12]infinitene dianion whether it sustains diatropic or paratropic ring currents. [ABSTRACT FROM AUTHOR]

A directly‐linked NiII porphyrin−NiII pyricorrole hybrid was obtained upon NiII complexation of internally‐bridged octaphyrin(1.1.1.1.1.1.1.1). The structure has been unambiguously revealed by X‐ray diffraction analysis. The pyricorrole skeleton is different from that reported earlier with regard to the position of the pyridine moiety. The new pyricorrole macrocycle was characterized as an aromatic molecule sustaining a complex current density. The thermodynamic stability of the NiII pyricorrole skeleton indicated by DFT calculation may drive this rearrangement. [ABSTRACT FROM AUTHOR]

Interactions of antimony‐oxide clusters with trypanothione have been modeled to understand their inhibitory activity against leishmaniasis. Trypanothione is essential for the survival of leishmania parasites because it is responsible for maintaining their cellular thiol‐disulfide redox regulation. Density functional theory calculations show that SbV oxide clusters form hydrogen bonds from the hydroxyl groups to the amine and carboxyl groups of the trypanothione. The reaction between trypanothione and the SbV oxide cluster does not break the SS bond of trypanothione, whereas a reaction between trypanothione and an antimony‐oxide cluster containing one SbIII atom may lead to dissociation of the SS bond of the trypanothione suggesting that antimony‐oxide clusters with at least one SbIII atom can destroy trypanothione that is vital for the parasite metabolism. [ABSTRACT FROM AUTHOR]