Magnetically Induced Ring-Current Strengths of Planar and Nonplanar Molecules: New Insights from the Pseudo-π Model

Abstract

The π-contribution to the magnetically induced current densities, ring-current strengths, and induced magnetic fields of large planar molecules (as kekulene) and three-dimensional molecules (as [10]cyclophenacene and chiral toroidal nanotubes C 2016 and C 2196 ) have been computed using the pseudo-π model with the gauge-including magnetically induced currents method. The magnetic response analysis shows that π-electrons are the main actors of the electron delocalization in carbon systems regardless of their size, suggesting that the π-component of the ring-current strengths can be used for assessing the aromatic character of this kind of molecules. Computations using the pseudo-π model yield current densities and induced magnetic fields that are not contaminated by contributions from core and σ-electrons allowing investigations of large molecular structures as polycyclic aromatic hydrocarbons and cylindrical or toroidal carbon nanotubes.File list (2) download file view on ChemRxiv pseudo_currents_main1_final_final.pdf (1.73 MiB) download file view on ChemRxiv pseudo_currents_SI.pdf (1.12 MiB)

The Magnetic Response of Starphenes

“…Previous studies on the π ring-current strength estimate a diatropic behavior of about 12 nA/T for benzene [10,34,35]. In this work, we estimate a value of 12.52 nA/T employing the pseudo-π model.…”

“…Consequently, the paratropic component of the strength is practically zero. For ring-current strengths caused by all electrons, the paratropic component is nonzero due to local σ-current loops in the C-C bonds [10,12,35]. The question arises as to how the magnetic response evolves when going from benzene to [4]starphene (triphenylene).…”

“…However, it is computationally demanding. It is possible for organic and all-carbon molecules to accurately approximate the magnetic response of the π-electrons via the pseudo-π model [10,17,18]. This strategy results from calculating the magnetic response of an optimized organic system by removing the hydrogens (if any), and the carbon centers are replaced by a set of hydrogen atoms in the same positions.…”

“…Aromaticity in PAHs is a key concept in understanding the electronic nature and bonding of these molecules [7][8][9]. Since aromaticity is related to the mobility of π-delocalized electrons, the study of the magnetic properties is attractive in starphenes because they may play a key role in their future electronic applications [10,11].…”

“…The magnetic response is studied by calculations of the magnetically induced current density [12][13][14][15][16] and the induced magnetic field. Given that the π-electron cloud is responsible for electron delocalization in these organic molecules, and the computational cost of computing these fields is expensive (especially when considering the separation of orbital contributions), we employ the pseudo-π model [17], which allows a precise and computationally cheap estimation of the π-component of the magnetic response in planar and non-planar organic and all-carbon structures [10,17,18]. Our results reveal that starphenes are prone to produce fully diatropic πcurrents.…”