Many foldamers, oligomers that adopt well-defined secondary structures, are now known, including many exhibiting functional behavior. However, examples of foldamer subunits within larger architectures remain rare, despite the importance of higher-order structure in biomacromolecules. Here, we investigate the dynamic covalent assembly of short o-phenylenes, a simple class of aromatic foldamers, into twisted macrocycles. o-Phenylene tetramers have been combined with rod-shaped p-phenylene-, tolane-, and diphenylbutadiyene-based linkers using imine formation. Macrocyclization proceeds efficiently, inducing folding of the o-phenylenes. The resulting [3 + 3] macrocycles (three o-phenylenes and three linkers) are shape-persistent, triangular structures with twisted cores and internal diameters up to approximately 2 nm. The homochiral D-symmetric and heterochiral C-symmetric conformers can be distinguished by NMR spectroscopy. Analysis of the conformational distribution for the p-phenylene-linked macrocycle suggests that the o-phenylene units are largely decoupled, with the less-symmetrical configuration therefore entropically favored. Conformational dynamics were assessed by variable-temperature NMR spectroscopy. Confinement within the macrocyclic architecture slows the inversion of the o-phenylene moieties.

The sizes and geometries of macrocycles assembled from ortho-phenylenes are predicted by the stabilities and bite angles of possible conformers.

Chiral groups induce opposite twist senses of o-phenylene helices depending on their positions in dynamic mixtures.

o-Phenylene tetramers have been coassembled with linkers into macrocycles through imine condensation. Variation of linker connectivity and length allows both [1 + 1] and [2 + 2] macrocycles to be obtained, complementing (previously reported) [3 + 3] macrocycles. For the [1 + 1] macrocycles, linker length has a clear effect on o-phenylene geometry and macrocycle stability. For the [2 + 2] macrocycles, both homo- and heterochiral configurations are observed, suggesting limited communication of helix handedness in these systems.

<p>Higher-order structure in abiotic foldamer systems represents an important but largely unrealized goal. As one approach to this challenge, covalent assembly can be used to assemble macrocycles with foldamer subunits in well-defined spatial relationships. Such systems have previously been shown to exhibit self-sorting, new folding motifs, and dynamic stereoisomerism, yet there remain important questions about the interplay between folding and macrocyclization and the effect of structural confinement on folding behavior. Here, we explore the dynamic covalent assembly of extended <i>ortho</i>-phenylenes (hexamer and decamer) with rod-shaped linkers. Characteristic ¹H chemical shift differences between cyclic and acyclic systems can be compared with computational conformer libraries to determine the folding states of the macrocycles. We show that the bite angle provides a measure of the fit of an <i>o</i>-phenylene conformer within a shape-persistent macrocycle, affecting both assembly and ultimate folding behavior. For the <i>o</i>-phenylene hexamer, the bite angle and conformer stability work synergistically to direct assembly toward triangular [3+3] macrocycles of well-folded oligomers. For the decamer, the energetic accessibility of conformers with small bite angles allows [2+2] macrocycles to be formed as the predominant species. In these systems, the <i>o</i>-phenylenes are forced into unusual folding states, preferentially adopting a backbone geometry with distinct helical blocks of opposite handedness. The results show that simple restrictions can be used to direct foldamers toward increasingly complex geometries.</p>

Fluorescent molecules and materials that exhibit emission changes in response to analytes are of great interest across multiple disciplines. Herein, we investigate the response of NHcontaining fluorophores carbazole and 2-phenylbenzimidazole (Ph-BIM) with two representative isolable singlet carbenes. Specifically, N-heterocyclic carbene 1,3-bis(2,6-diisopropylphenyl)imidazol-2ylidene (IPr) and cyclic (alkyl)(amino)carbene (2,6-diisopropylphenyl)-4,4-diethyl-2,2-dimethyl-pyrrolidin-5-ylidene ( Et CAAC) were discovered to afford three different types of reaction products with carbazole and Ph-BIM. Depending on the reaction pair, hydrogen bonding (1), NH-insertion (2,3), or proton transfer (4) products can be isolated, each displaying variable photophysical responses. These products have been structurally authenticated by single crystal X-ray diffraction and NMR spectrometric methods. Studies of the solution state behavior of 1−4 reveals that these adducts are labile and can reversibly dissociate to free carbenes and fluorophores to varying extents. These equilibria produce concentration dependent solution state behavior as identified and quantified via UV−visible absorption, emission, 1 H DOSY, and NMR spectroscopic measurements.

<p>Higher-order structure in abiotic foldamer systems represents an important but largely unrealized goal. As one approach to this challenge, covalent assembly can be used to assemble macrocycles with foldamer subunits in well-defined spatial relationships. Such systems have previously been shown to exhibit self-sorting, new folding motifs, and dynamic stereoisomerism, yet there remain important questions about the interplay between folding and macrocyclization and the effect of structural confinement on folding behavior. Here, we explore the dynamic covalent assembly of extended <i>ortho</i>-phenylenes (hexamer and decamer) with rod-shaped linkers. Characteristic ¹H chemical shift differences between cyclic and acyclic systems can be compared with computational conformer libraries to determine the folding states of the macrocycles. We show that the bite angle provides a measure of the fit of an <i>o</i>-phenylene conformer within a shape-persistent macrocycle, affecting both assembly and ultimate folding behavior. For the <i>o</i>-phenylene hexamer, the bite angle and conformer stability work synergistically to direct assembly toward triangular [3+3] macrocycles of well-folded oligomers. For the decamer, the energetic accessibility of conformers with small bite angles allows [2+2] macrocycles to be formed as the predominant species. In these systems, the <i>o</i>-phenylenes are forced into unusual folding states, preferentially adopting a backbone geometry with distinct helical blocks of opposite handedness. The results show that simple geometric restrictions can be used to direct foldamers toward increasingly complex geometries.</p>

In general, ortho-phenylene hexamers are not good substrates for oxidative planarization because of competing backbone rearrangements. However, by first planarizing the ends, a target tetrabenzanthanthrene has been obtained by oxidation in good yield. DFT calculations suggest that the larger polycyclic aromatic subunits of the preplanarized substrate increase the rate of planarization relative to that of rearrangement. By implication, it may be possible to prepare graphene structures that cannot be made directly from simple polyphenylenes by instead designing precursors with larger polycyclic aromatic moieties. The photophysical properties of the tetrabenzanthanthrene core indicate that it may have promise as a functional chromophore.