The chemistry of a belt-shaped cyclic array of aromatic panels, a socalled "nanohoop," has increasingly attracted much interest, partly because it serves as a segmental model of single-wall carbon nanotubes with curved sp 2 -carbon networks. Although the unique molecular structure of nanohoops is expected to deepen our understanding in curved π-systems, its structural chemistry is still in its infancy despite structural variants rapidly accumulated over the past several years. For instance, structural characteristics that endow the belt shapes with rigidity, an important structural feature relevant to carbon nanotubes, have not been clarified to date. We herein report the synthesis and structures of a series of belt-shaped cyclonaphthylenes. Random synthesis methods using three precursor units with different numbers of naphthylene panels allowed us to prepare 6 congeners consisting of 6 to 11 naphthylene panels, and relationships between the rigidity and the panel numbers, i.e., molecular structures, were investigated. Fundamental yet complicated stereoisomerism in the belt-shaped structures was disclosed by mathematical methods, and dynamics in the panel rotation was revealed by dynamic NMR studies with the aid of theoretical calculations.T he chemistry of hoop-shaped cycloarylenes (nanohoops) is being enriched by increasing variations in the molecular structures (1-4). The structural diversity in the constitutional arylene panels has gradually increased by starting from cyclopara-phenylenes (CPP; Fig. 1) with the most primordial panel being benzene (5-7), and the nanohoop chemistry is deepening our understanding of π-conjugated structures with belt-shaped, curved sp 2 -carbon networks that mimic single-wall carbon nanotubes (SWNTs) (8).Composed of arylene panels connected via multiple singlebond linkages, the belt-shaped nanohoop structures pose a fundamental and important question related to the isomerism and persistency of the curved sp 2 -carbon networks (8). Previously, we synthesized the first, to our knowledge, belt-persistent nanohoops to demonstrate that large arylene panels, such as chrysene and anthanthrene, endowed the nanohoop molecules with belt persistency. The belt-shaped atropisomers of [4]cyclochrysenylenes ([4]CC) (9, 10) and [4]cycloanthanthrenylenes ([4]CA) (11) were separated and identified as discrete molecular entities (Fig. 1), and the atropisomerism uniquely originated from restricted sp 2 -sp 2 rotations due to macrocyclic ring strain (12). However, the experimental relationship between the structure and dynamics of the arylene rotations in the nanohoops remains unclear (13-16) and will add novel insight to biaryl atropisomerism with structural and historical importance (17-20). We herein report our first attempt to reveal the structure-dynamics relationship in belt-shaped nanohoop molecules via the synthesis of a series of [n]cyclo-amphi-naphthylenes ([n]CaNAP, n = 6-11; Fig. 1) (21). Albeit simple at first glance, the molecular structures were rich in structural chemistry including ...

The recent development of cyclo-para-phenylenes has demonstrated the feasibility of radial π systems in nanohoop structures, especially in the crystalline state. However, in contrast to macrocyclic molecules with benzene units, which have a several-decades-long history, macrocycles composed solely of naphthylene units (the smallest acene) have been much less explored. Although two examples of cyclonaphthylenes have been reported to date, neither possesses a radial π system. We herein report the first example of belt-shaped cyclonaphthylenes with curved π systems. The molecule, [8]cyclo-amphi-naphthylene, is linked at the 2,6-positions of the naphthylene units, thus affording belt-shaped molecules. Although the molecular structures are flexible, which allows for rotation of the naphthylene units in solution, they can be rigidified with the aid of methylene bridges to afford persistent molecular structures in solution.

The stereochemistry of cycloarylene nanohoops gives rise to unique cyclostereoisomerism originating from hoop-shaped molecular shapes. However, cyclostereoisomerism has not been well understood despite the ever-increasing number of structural variants. The present work clarifies the cyclostereoisomerism of a cyclophenanthrenylene nanohoop possessing both E/Z- and R/S-geometries at the biaryl linkages. Involvement of the R/S axial chirality in the nanohoop leads to the deviation of the structure from a coplanar belt shape and allows for structural variations with 51 stereoisomers with E/Z- and R/S-geometries. Experimental investigations of the dynamic behaviors of the cyclophenanthrenylene nanohoop revealed the presence of two-stage isomerization processes taking place separately at the E/Z- and R/S-linkages. Consequently, despite the presence of E/Z-fluctuations, the R/S axial chirality resulted in a separable pair of enantiomers. The structural information reported here, such as geometric descriptors and anomalous dynamics, may shed light on the common structures of various nanohoops.

Twofold Perkin condensation of 2,5-dibromophenylene-1,4-diacetic acid with arylglyoxylic acids followed by cyclo-dehydrobromination leads to dipyreno- and diperyleno-anthracene tetraesters and diimides. The imides show surprisingly large absorption shifts versus the esters, illustrating that electron-withdrawing substituents at the anthracene unit efficiently impart long wavelength absorption in such electron-deficient graphene nanoribbon fragments.