Helicenes consist of several fused rings twisted around an axis, forming a cylindrical helix, with π‐delocalized electrons in the non‐planar rings. Induced magnetic fields dissecting the orbital ...contributions of 6‐, 7‐, and 14helicene are discussed. Computations show a deshielding cone produced by the π‐electrons along the helical axis. Unexpectedly, the response of the core electrons produces a shielding cone, which is cumulative and sensitive to the curvature of the systems owing to the overlap of the other ring responses. A warning is provided regarding the evaluation of the delocalization in curved systems in which the x‐ and y‐components of the induced magnetic field become relevant.
Induced magnetic fields dissecting the orbital contributions of 6‐, 7‐, and 14helicene are discussed. Computations show a deshielding cone produced by the π‐electrons along the helical axis. Unexpectedly, the response of the core electrons produces a shielding cone, which is cumulative and sensitive to the curvature of the systems owing to the overlap of the other ring responses.
ABSTRACT
Spherical fullerenes offer noteworthy structures usually involving six‐ and five‐membered faces, with application in technological issues. In this sense, cavernous spherical‐like structures ...bearing larger holes provide interesting examples for further understanding of structure‐properties relationship. Here, we explored the magnetic response of a proposed cavernous nitride fullerene, C24N24, which has a Oh‐symmetry with six N4‐macrocyclic and eight 1,3,5‐triazine faces displaying 48‐π electrons. C24N24 exhibits a local aromatic behavior owing to the contrasting antiaromatic response of the N4‐macrocyclic faces and the aromatic character of the 1,3,5‐triazine faces. Thus, the overall structure is ascribed as a local aromatic species, where the triazine faces exhibit the characteristic shielding cone for aromatic rings. Furthermore, the constructive combination of local shielding cones in C24N24 delivers a related shielding‐cone response, as expected for a perfect aromatic cage. Hence, the local aromatic/nonaromatic/antiaromatic sections exhibit an additive or subtractive interaction, leading to a characteristic response inherent to the nature of the spherical cage. We expect that further study of the interplay between different aromatic and antiaromatic faces in fullerene‐like cages can deliver interesting pseudo‐aromatic or pseudo‐antiaromatic spherical species.
N4‐Cavernous fullerene‐like structures show an interesting example of local‐aromatic species building up a global magnetic response.
The electron delocalization in 1,2-azaborine, 1,3-azaborine, and 1,4-azaborine is studied using canonical molecular orbital contributions to the induced magnetic field (CMO-IMF) method and ...polyelectron population analysis (PEPA). Contour maps of the out-of-plane component of the induced magnetic field (B z ind) of the π system show that the three azaborines, in contrast with borazine, sustain much of benzene’s π-aromatic character. Among them, 1,3-azaborine exhibits the strongest π delocalization, while 1,4-azaborine is the weakest. Contour maps of B z ind for individual π orbitals reveal that the differentiation of the magnetic response among the three isomers originates from the π-HOMO orbitals, whose magnetic response is governed by rotational allowed transitions to unoccupied orbitals. The low symmetry of azaborines enables a paratropic response from HOMO to unoccupied orbitals excitations, with their magnitude depending on the shape of interacting orbitals. 1,3-Azaborine presents negligible paratropic contributions to B z ind from HOMO to unoccupied orbitals transitions, where 1,2- and 1,4-azaborine present substantial paratropic contributions, which lead to reduced diatropic response. Natural bond orbital (NBO) analysis employing PEPA shows that only the 1,3-azaborine contains π-electron fully delocalized resonance structures.
Endohedral metallofullerenes are key species for expanding the range of viable fullerenes, their versatility, and applications. Here we report our computational evaluation on the formation of ...spherical aromatic counterparts of the C60 fullerene from relativistic DFT calculations, based on the inclusion of Cr, Mo and W endohedral atoms. The resulting M@C60 endohedral fullerenes are 66-π electron neutral species exhibiting bonding properties and electronic structure mimicking the aromaticity and diamagnetic insulator behavior of alkali-C606− phases. The resulting structures are interesting candidates for further experimental realization as novel neutral building blocks for more flexible nanostructured organic materials, highlighting truly spherical aromatic neutral species retaining the truncated icosahedral structure of the seminal Buckminster fullerene.
The induced magnetic field of B
40
was dissected into contributions from π, σ and core electrons revealing the origins for the formation of the strong long range shielding response characterizing the ...spherical aromatic nature of the cavernous
D
2d
structure. Our analysis showed the complementary role of π and σ orbitals for the formation of the global shielding cone, with weak π contributions at a long range and strong σ contributions inside the cage, supporting the molecule as double aromatic with weak π and strong σ delocalization. Similar local variations of both π and σ magnetic responses were identified portraying peripheral diatropic and local paratropic currents. The weak π aromaticity is explained on the basis of symmetry rules pertaining to its electronic structure which forbid small gap paratropic rotational excitations.
B
40
enables the formation of a strong long range shielding response under different orientations, characterizing the spherical aromatic nature of the cavernous
D
2d
structure, which was dissected to contributions from π, σ and core electrons.
Materials combining amplified nonlinear optical responses and wide optical gaps that ensure high laser-induced damage thresholds and broadband transparency are highly required for photonic ...applications. In this article, we use well-established quantum chemical methods to demonstrate that a special class of polyaromatic hydrocarbons, in which multiple borazine (B3N3) units substitute aromatic carbon sextets, are suitable for the design and synthesis of systems meeting both above requirements. Computations conducted in a wide assortment of purposely designed nanographene model systems exposed robust doping/property relations which point out that multiple B3N3 doping can be considered as an efficient strategy to enhance the quadratic nonlinear optical responses of a given polyaromatic hydrocarbon maintaining at the same time wide optical gaps. A detailed analysis of the underlying charge transfer mechanism revealed that the observed features stem from local in character electronic excitations occurring between the incorporated B3N3 units and neighboring aromatic sextets.
Endohedral metallofullerenes are key species for expanding the range of viable fullerenes, their versatility, and applications. Here we report our computational evaluation on the formation of ...spherical aromatic counterparts of the C
60
fullerene from relativistic DFT calculations, based on the inclusion of Cr, Mo and W endohedral atoms. The resulting M@C
60
endohedral fullerenes are 66-π electron neutral species exhibiting bonding properties and electronic structure mimicking the aromaticity and diamagnetic insulator behavior of alkali-C
60
6−
phases. The resulting structures are interesting candidates for further experimental realization as novel neutral building blocks for more flexible nanostructured organic materials, highlighting truly spherical aromatic neutral species retaining the truncated icosahedral structure of the seminal Buckminster fullerene.
The resulting M@C
60
endohedral fullerenes are 66-π electron neutral species exhibiting bonding properties and electronic structure mimicking the aromaticity and diamagnetic insulator behavior of alkali-C
60
6−
phases.
Endohedral metallofullerenes are key species for expanding the range of viable fullerenes, their versatility, and applications. Here we report our computational evaluation on the formation of ...spherical aromatic counterparts of the C 60 fullerene from relativistic DFT calculations, based on the inclusion of Cr, Mo and W endohedral atoms. The resulting M@C 60 endohedral fullerenes are 66-π electron neutral species exhibiting bonding properties and electronic structure mimicking the aromaticity and diamagnetic insulator behavior of alkali-C 60 6− phases. The resulting structures are interesting candidates for further experimental realization as novel neutral building blocks for more flexible nanostructured organic materials, highlighting truly spherical aromatic neutral species retaining the truncated icosahedral structure of the seminal Buckminster fullerene.
