para‐Verknüpfte Cyclophenylene und halbkugelförmige Polyarene: Bausteine für einwandige Kohlenstoffnanoröhren?

Abstract

Kohlenstoffnanoröhren durch Design? Cyclo‐para‐phenylene sind Monomere für die Synthese von Lehnsessel‐Kohlenstoffnanoröhren (rechts im Bild) und zudem vielversprechende Fluorophore mit größenabhängigen Emissionseigenschaften. Geodäsische Polyarene bieten eine interessante Alternative für den rationalen Aufbau von Kohlenstoffnanoröhren durch chemische Verlängerung der gekrümmten Kohlenwasserstofftemplate (links).

Properties of Sizeable [n]Cycloparaphenylenes as Molecular Models of Single‐Wall Carbon Nanotubes Elucidated by Raman Spectroscopy: Structural and Electron‐Transfer Responses under Mechanical Stress

“…Figure 2 shows the 785 nm excitation Raman spectra for the seven [n]CPP compounds. We noticed that the two bands above are predicted at 274 and 233 cm À1 in [10]CPP and [12]CPP (Supporting Information, Figures S2.1, S3.1, and S.4.1 and Tables S2.1, S3.1, and S4.1); however, correspond to E 2g or E 2 symmetry modes, thus not representing true RBM modes, which are totally symmetric modes. To check this hypothesis, we have carried out quantum chemical calculations of the vibrational Raman spectra for the most stable conformers of the [n]CPPs (Supporting Information, Section S1).…”

“…Frequencies were scaled with the uniform scaling factor of 0.97. The low wavenumber regions of [10]CPP and [12]CPP are clearly dominated by single bands at 286 and 242 cm À1 , respectively, that would belong in principle to RBM radial-like modes. The low wavenumber regions of [10]CPP and [12]CPP are clearly dominated by single bands at 286 and 242 cm À1 , respectively, that would belong in principle to RBM radial-like modes.…”

“…[2a, 10] In our interest of exploring possible mechanical, chemical and spectroscopic analogies between [n]CPPs and SWCNTs, we here study [n]CPPs in an oligomeric approach to SWCNTs. Furthermore, [n]CPPs are significant on their own right given their salient optoelectronic and structural properties, [3][4][5][6][7][8][9]11] and their host-guest ability to form supramolecular assemblies [7,12] (van der Waals nanotubes). Furthermore, [n]CPPs are significant on their own right given their salient optoelectronic and structural properties, [3][4][5][6][7][8][9]11] and their host-guest ability to form supramolecular assemblies [7,12] (van der Waals nanotubes).…”

“…[6]CPP to [12]CPP, aiming to get new structural and chemical insights within the context of molecular strain, peripheral or cyclic p-electron delocalization, mechanical flexibility, and host-guest properties. The latter aspect deserves special mention, as we have realized a novel full charge-transfer host-guest complex between [10]CPP and C 60 promoted under high pressure, which contrasts with that well-known supramolecular complex solely formed by p···p van der Waals concave-convex interactions.…”

“…[16,17] However, no G À modes are recognized owing to the absence of a well-defined longitudinal direction in the [n]CPPs (Supporting Information, Tables S2.1 and S3.1). The Raman band at 1567 cm À1 indicates a benzoquinonoid structure and strong cycle strain in [6]CPP, while that at 1595 cm À1 in [12]CPP reveals a slightly curved macrocycle with a ring aromatic character similar to that of linear oligoparaphenylenes (Supporting Information, Figure S5.1 and Table S5.1). It is well known that 8a mode frequencies around 1600 cm À1 are characteristic of benzo-aromatic moieties, while down-shifted frequencies are typical of benzoquinonoid moieties.…”