Carbon nanotubes (CNTs) interlocked by cyclic compounds through supramolecular interaction are promising rotaxane-like materials applicable as 2D and 3D networks of nanowires and disease-specific theranostic agents having multifunctionalities. Supramolecular complexation of CNTs with cyclic compounds in a "ring toss'' manner is a straightforward method to prepare interlocked CNTs; however, to date, this has not been reported on. Here, the "ring toss" method to prepare interlocked CNTs by using π-conjugated carbon nanorings: [8]-, [9]-, and [10]cycloparaphenyleneacetylene (CPPA) is reported. CPPAs efficiently interact with CNTs to form CNT@CPPA complexes, while uncomplexed CPPAs can be recovered without decomposition. CNTs, which tightly fit in the cavities of CPPAs through convex-concave interaction, efficiently afford "tube-in-ring"-type CNT@CPPA complexes. "Tube-in-ring"-type and "ring-on-tube"-type complexation modes are successfully distinguished by spectroscopic, thermogravimetric, and microscopic analyses.
Carbon‐based double helicates consisting of two anthracene‐containing oligo(p‐phenyleneethynylene) units and two flexible chiral 1,1′‐binaphthyl units or two rigid chiral 9,9′‐spirobifluorene units were developed. The curved oligo(p‐phenyleneethynylene) fragments in the double helicates were successfully constructed by tin‐mediated reductive aromatization. Helical oligo(p‐phenyleneethynylene) double strands fixed by two rigid spirobifluorene units showed little structural change under photoirradiation, thereby emitting circularly polarized luminescence (CPL) in the visible region with a high quantum yield (ΦPL=0.93). In contrast, flexible binaphthyl units induced dynamic structural change of the oligo(p‐phenyleneethynylene) luminophores under photoirradiation, leading to strong CPL (|glum|=1.1×10−2) in the near‐infrared (NIR) region. UV/Vis, circular dichroism (CD), CPL and NMR spectroscopic analyses of the binaphthyl‐hinged double helicate suggested excimer formation between two π‐conjugated strands in the excited state. Theoretical calculations highlight the importance of the tightly interlocked excimer structure of the carbon‐based double helicate in controlling the angle between the electric and magnetic transition dipole moments for strong NIR CPL generation.
In article number https://doi.org/10.1002/smll.201800720, Koji Miki, Kouichi Ohe, and co‐workers report the “ring toss” method, throwing carbon nanorings onto carbon nanotubes, to prepare “tube‐in‐ring” supramolecular complexes. Carbon nanorings, [n]cycloparaphenyleneacetylenes, are utilized to demonstrate the formation of “tube‐in‐ring” complexes. The good size fit between the concave inner surface of the carbon nanorings and the convex outer surface of carbon nanotubes is important for the efficient production of rotaxane‐like complexes. This work provides a strategy to prepare interlocked carbon nanotubes for next‐generation electric devices and theranostic agents.
Carbon‐based double helicates consisting of oligo(p‐phenyleneethynylene)s and “flexible” 2,2’‐binaphthyls or “rigid” 9,9′‐spirobifluorenes were synthesized. The “rigid” double helicate acts as a bright macrocyclic fluorophore. The “flexible” double helicate forms a tightly interlocked intramolecular excimer under photoirradiation, emitting near‐infrared circularly polarized luminescence with high dissymmetry factor value. More information can be found in the Full Paper by K. Miki, K. Ohe, et al. on page 9211.
Invited for the cover of this issue is the group of Koji Miki, Kouichi Ohe, and colleagues at Kyoto University. The image depicts mythical dragons as carbon‐based double helicates. Read the full text of the article at 10.1002/chem.201901467.
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