Cycloparaphenylenes (CPPs) exhibit selective host capabilities, featuring the ability to incorporate smaller CPPs to form double-walled host-guest complexes. Moreover, CPPs can also be stabilized by ...global aromaticity under twofold oxidation or reduction, involving electronic conjugation along with the overall structural backbone. Herein we explore the structural modifications, bonding, electron delocalization and magnetic properties of doubly reduced double-walled CPP complexes with DFT methods, in the isolated and aggregate
n
+ 5CPP⊃
n
CPP
2−
(
n
= 5-8) species. Our results show that the hosts undergo structural, bonding and delocalization deformations towards quinoidal configurations and exhibit global long-ranged shielding cones similar to global aromatic free dianionic CPPs, accounting for charge delocalization on the outer nanohoops, whereas the guests preserve local aromatic benzenoid configurations, resulting in global and local aromatic circuits within the host-guest aggregate. This observation suggests that in multi-layered related species electronic delocalization will be retained at the outer structural surface. The aromaticity of the hosts is manifested in the strong upfield shifts of the guests
1
H-NMR signals. Hence, CPP complexes can be extended to doubly reduced species stabilized by global host aromaticity expanding our understanding of doubled-walled nanotubes at the nanoscale regime.
The charge is delocalized on the outer nanohoop of double-walled doubly reduced
n
+ 5CPP⊃
n
CPP
2−
complexes enabling global host aromaticity which strongly shields the guests delivering upfield
1
H-NMR chemical shifts.
Nanoscaled 2D and 3D carbon structures with closed curved π-surfaces are of relevance in the development of desirable building units for materials science. Such species are able to sustain local and ...global aromatic circuits involving isolated regions or the overall structural backbone, respectively. Here we account for local and global aromaticity under rotation of representative two- and three-dimensional species involving
para
-connected and fused edge-sharing phenyl rings (8CPP, 10CPP, CNB), and C
60
fullerene at different charge states. Our results denote that nanoscaled 2D global aromatics mimic the behaviour of the most prototypical aromatic 6π-circuit, given by benzene, where the shielding cone properties vary along the rotation motion. In contrast, 3D spherical aromatics remain almost invariant under rotation, given the distinctive characteristics of such species, differing from 2D global aromatics. Dissection of orbital contributions reveals that π-orbitals are determinants for shifting from non-aromatic to spherical aromatic species. Under rotation, the variation of the anisotropic effect inherent to such nanoscaled structures is accounted for, which is relevant to rationalize variation in NMR signal shifts upon the formation of host-guest aggregates.
Nanoscaled 2D and 3D carbon structures with closed curved π-surfaces are of relevance in the development of desirable building units for materials science, where the connection between small and larger molecular systems is revealed.
Dications of cycloparaphenyles (nCPPs) are known to exhibit in‐plane global aromaticity, contained in a nanobelt structure. Recently synthesized ortho and meta isomers of nCPPs break the radial ...symmetry of π structure incorporating perpendicular oriented π orbitals. Herein we set to explore the aromaticity of neutral and dicationic ortho and meta isomers of 8CPP by dissecting the induced magnetic field to contributions of the twofold radial/perpendicular π system using delocalized canonical molecular orbitals (CMO), and introducing the natural localized molecular orbitals (NLMO) analysis with DFT methods. The dications sustain a reduced global aromatic character of the radial π system under a perpendicular orientation of the external field which declines from ortho to meta isomer and reinforces local aromaticity of ortho ring while it destroys aromaticity of meta ring. Aromaticity variations are determined by symmetry governed rotational excitations of frontier π orbitals. The parallel orientation reveals a substantial reduction of local aromaticity verified with NICSπ analysis and electron delocalization indices.
How aromatic? Ortho and meta isomers of the 8‐clycloparaphenylene dication retain a decreasing global aromatic character of the twofold radial‐perpendicular π system, while local aromaticity is augmented in the ortho ring and becomes antiaromatic in meta ring.
