[2.2.2.2]Paracyclophanetetraenes (PCTs): cyclic structural analogues of poly(p‑phenylene vinylene)s (PPVs)

Background: Poly(p-phenylene vinylene)s (PPVs) and [2.2.2.2]paracyclophanetetraene (PCT) are both composed of alternating π-conjugated para-phenylene and vinylene units. However, while the former constitute a class of π-conjugated polymers that has been used in organic electronics for decades, the latter is a macrocycle that only recently revealed its potential for applications such as organic battery electrodes. The cyclic structure endows PCT with unusual properties, and further tuning of these may be required for specific applications. Methods: In this article, we adopt an approach often used for tuning the properties of PPVs, the introduction of alkoxy (or alkylthio) substituents at the phenylene units, for tuning the optoelectronic properties of PCT. The resulting methoxy- and methylthio-substituted PCTs, obtained by Wittig cyclisation reactions, are studied by UV-vis absorption, photoluminescence, and cyclic voltammetry measurements, and investigated computationally using the visualisation of chemical shielding tensors (VIST) method. Results: The measurements show that substitution leads to slight changes in terms of absorption/emission energies and redox potentials while having a pronounced effect on the photoluminescence intensity. The computations show the effect of the substituents on the ring currents and chemical shielding and on the associated local and global (anti)aromaticity of the macrocycles, highlighting the interplay of local and global aromaticity in various electronic states. Conclusions: The study offers interesting insights into the tuneability of the properties of this versatile class of π-conjugated macrocycles.

A Volumetric Analysis of the 1H NMR Chemical Shielding in Supramolecular Systems

The liquid state NMR chemical shift of protons is a parameter frequently used to characterize host–guest complexes. Its theoretical counterpart, that is, the 1H NMR chemical shielding affected by the solvent (1H CS), may provide important insights into spatial arrangements of supramolecular systems, and it can also be reliably obtained for challenging cases of an aggregation of aromatic and antiaromatic molecules in solution. This computational analysis is performed for the complex of coronene and an antiaromatic model compound in acetonitrile by employing the GIAO-B3LYP-PCM approach combined with a saturated basis set. Predicted 1H CS values are used to generate volumetric data, whose properties are thoroughly investigated. The 1H CS isosurface, corresponding to a value of the proton chemical shift taken from a previous experimental study, is described. The presence of the 1H CS isosurface should be taken into account in deriving structural information about supramolecular hosts and their encapsulation of small molecules.

The relationships between atomic charges and magnetic response properties reflects conductivity of BN nanotubes

In this work, the potential relation between magnetic response properties (isotropic shielding (σ) and total atomic magnetizabilities, Χ(Ω)) with QTAIM atomic charges of boron and nitrogen atoms in (4,4), (5,3) and (7,0) single-walled boron nitride nanotubes (SWBNNTs) are investigated at DFT B3LYP/ 6-31G(d) level of theory using periodic boundary condition (PBC) approach. The results show that a liner correlation exists between atomic charges of B and N in (4,4) and (5,3) BNNTs and the isotropic shielding. The results show a solid correlation between chemical shielding and total-atomic magnetizabilities, Χ(Ω) in (4,4) BNNT with the lowest conductivity.

Visualisation of Chemical Shielding Tensors (VIST) to Elucidate Aromaticity and Antiaromaticity

Aromaticity is a central concept in chemistry, pervading areas from biochemistry to materials science. Recently, chemists also started to exploit intricate phenomena such as the interplay of local and global (anti)aromaticity or aromaticity in non-planar systems and three dimensions. These phenomena pose new challenges in terms of our fundamental understanding and the practical visualisation of aromaticity. To overcome these challenges, a method for the visualisation of chemical shielding tensors (VIST) is developed here that allows for a 3D visualisation with quantitative information about the local variations and anisotropy of the chemical shielding. After exemplifying the method in different planar hydrocarbons, we study two non-planar macrocycles to show the unique benefits of the VIST method for molecules with competing pi-conjugated systems and conclude with a norcorrole dimer showing clear evidence of through-space aromaticity. We believe that the VIST method will be a highly valuable addition to the computational toolbox.

Visualisation of Chemical Shielding Tensors (VIST) to Elucidate Aromaticity and Antiaromaticity

Aromaticity is a central concept in chemistry, pervading areas from biochemistry to materials science. Recently, chemists also started to exploit intricate phenomena such as the interplay of local and global (anti)aromaticity or aromaticity in non-planar systems and three dimensions. These phenomena pose new challenges in terms of our fundamental understanding and the practical visualisation of aromaticity. To overcome these challenges, a method for the visualisation of chemical shielding tensors (VIST) is developed here that allows for a 3D visualisation with quantitative information about the local variations and anisotropy of the chemical shielding. After exemplifying the method in different planar hydrocarbons, we study two non-planar macrocycles to show the unique benefits of the VIST method for molecules with competing pi-conjugated systems and conclude with a norcorrole dimer showing clear evidence of through-space aromaticity. We believe that the VIST method will be a highly valuable addition to the computational toolbox.

3D Visualisation of Chemical Shielding Tensors (VIST) to Elucidate Aromaticity and Antiaromaticity

Aromaticity is a central concept in chemistry, pervading areas from biochemistry to materials science. Recently, synthetic chemists started to exploit more intricate phenomena such as the interplay of local and global (anti)aromaticity as well as aromaticity in non-planar systems and three dimensions. These phenomena pose new challenges in terms of our fundamental understanding and the practical visualisation of aromaticity, its local variations and anisotropy. To overcome these challenges, a method for the visualisation of chemical shielding tensors (VIST) is developed here. The VIST method is based on nucleus-independent chemical shifts but, in contrast to other methods, allows for a 3D visualisation with quantitative information about the local variations and anisotropy of the chemical shielding. The VIST method is exemplified in benzene to show its main properties, in phenanthrene to highlight various degrees of local aromaticity, and in cyclobuta[l]phenanthrene to illustrate the interplay between local aromaticity and antiaromaticity in its singlet ground state and Baird aromaticity in its triplet excited state.<br>Subsequently, the interplay of local and global aromaticity is investigated in two non-planar macrocycles, paracyclophanetetraene and [8]cycloparaphenylene, exemplifying the unique benefits of the VIST method for studying (anti)aromaticity in molecules with competing $\pi$-conjugated systems aligned in different planes.<br>Finally, a stacked norcorrole dimer is studied, showing clear evidence of through-space aromaticity. In summary, we believe that the VIST method will be a highly valuable addition to the computational toolbox of chemists studying (anti)aromaticity or considering it in their molecular design.

Drug delivery via super-paramagnetic (N2)n[SiO2(OH)2]8 Core-Shell catalyst

The MNPs @ [SiO2(OH)2]8 catalyzers were stablished via ab-initio and quantum mechanics & Molecular mechanic (QM/MM) simulation. The studies focus on how to improve the dispersion of composite particle for achieving high magnetic performances. The results revealed that the Fe3O4 @[SiO2 (OH)2]8(N2)8 as a cabalist exhibited better thermodynamic stability and dispersion than the magnetite nanoparticles. Furthermore, the particle size and magnetic properties of the [SiO2 (OH)2]8(N2)8 composite nanoparticles can be controlled by changing the functional groups. The electrical properties such as NMR Shielding, electron densities, energy densities, potential energy densities, ELF, LOL, of electron density, eta index, ECP, ESR and hyperfine interactions for Fe3O4@ [SiO2(OH)2]8(N2)8 have been calculated. As the catalyst could be easily recovered by magnetic separation and recycled for a few times without significant loss of its catalytic activity, we have calculated to obtain the stronger non bonded interaction in the Fe3O4@ [SiO2(OH)2]8(N2)8 system. This system can be used for antibiotics drug delivery instead of injection. The chemical shielding and several factors as the same electronegativity, magnetic anisotropy of π-systems will be changed due to the number of electrons The chemical shielding is a vector orientation function for all of the shielding parameters that can change in several places inside the shielding region.