An Obtuse‐angled Corner Unit for Fluctuating Carbon Nanohoops

Abstract

The invention of corner units was the key factor that allowed the synthesis of cyclo-para-phenylenes with strained curved π-systems. Despite only a few scarce instances of the development of corner units to date, a variety of structural congeners have been synthesized. These preceding corner units commonly possessed directing angles of ≤90°, which enabled the macrocyclization of multiple units, up to six. In this study, we introduce an obtuse-angled corner unit for the synthesis of cyclo-para-phenylene congeners. The corner unit with oxanorbornadiene possessed a directing angle of 126° and thus allowed for the macrocyclization of larger structures with up to seven units. Reductive aromatization was applicable to complete the cyclo-para-phenylene structures and afforded the congeners with multiple anthracenylene panels. Structural studies with experimental and theoretical methods revealed a fluctuating structure with an intrinsic non-belt shape.

Pentagon‐Embedded Cycloarylenes with Cylindrical Shapes

“…Ther ed shift of [3]CR was larger,s howing a + 140 nm shift for the onset absorption. [34] These cycloarylenes possess the same p-systems as the present [n]CR molecules but lack the pentagon bridges in the cyclic structures.T hus,b ased on this comparison, we can conclude that the p-conjugation is extended over the pentagon bridges as well as the biaryl linkages in the [n]CR molecules.A nother difference that resulted from the presence of the pentagons was noted in the fluorescence spectra. [32,33] This result shows that the p-conjugate system is extended in [n]CR from the monomeric rubicene.P reviously,w eh ave shown that relevant cycloarylenes with phenylene/anthracenylene panels commonly exhibit an onset absorption maximum at approximately 400 nm, independent of the number of panels.…”

“…TheA AA orientation of the rubicene panels that had been suggested by the solution-phase NMR analysis was thus confirmed. [34] Analyses of the bond lengths indicated that the quinoidal character was enhanced in the cylinder-shaped structure.F or instance,t he CÀCbond of [3]CR connecting C6 and C7 was shortened by 0.03 ,whereas the C4ÀC5 and C5ÀC6 bonds were extended by 0.04 (see Scheme 1f or the position numbers). [21] Ah armonic oscillator model of aromaticity (HOMA) was obtained from the crystal structures of [3]CR and rubicene.…”

Pentagon‐Embedded Cycloarylenes with Cylindrical Shapes

“…[32,33] This result shows that the p-conjugate system is extended in [n]CR from the monomeric rubicene.P reviously,w eh ave shown that relevant cycloarylenes with phenylene/anthracenylene panels commonly exhibit an onset absorption maximum at approximately 400 nm, independent of the number of panels. [34] These cycloarylenes possess the same p-systems as the present [n]CR molecules but lack the pentagon bridges in the cyclic structures.T hus,b ased on this comparison, we can conclude that the p-conjugation is extended over the pentagon bridges as well as the biaryl linkages in the [n]CR molecules.A nother difference that resulted from the presence of the pentagons was noted in the fluorescence spectra. The[ n]CR molecules were not fluorescent whereas the phenylene/anthracenylene cycloarylenes without pentagons do fluoresce.The effect of the pentagons on the excited states is of interest for further investigations in the future.…”

“…[36] Another comparison of the HOMA values with relevant phenylene/anthracenylene cycloarylenes showed that the conjugation via pentagon bridges was also important for this reduced aromaticity ( Figure S3). [34] Analyses of the bond lengths indicated that the quinoidal character was enhanced in the cylinder-shaped structure.F or instance,t he CÀCbond of [3]CR connecting C6 and C7 was shortened by 0.03 ,whereas the C4ÀC5 and C5ÀC6 bonds were extended by 0.04 (see Scheme 1f or the position numbers).…”

Narrowing Segments of Helical Carbon Nanotubes with Curved Aromatic Panels

“…Arylene panel structures play key roles in deciding the numbers of panels participating in macrocyclization, and during our synthetic study of a sextuply helical molecule, we realized that a contorted aromatic panel of dibenzochrysene (denoted db C) could tune the panel numbers to form a narrow cylindrical macrocycle composed of chrysenylene units. Thus, in the db C panel, two boryl linkers were first installed at its 3,11‐positions via an 8‐step synthetic process starting from a commercially available compound (Figure ).…”