Size- and Orientation-Selective Encapsulation of C70 by Cycloparaphenylenes

The size‐ and orientation‐selective formation of the shortest‐possible C70 peapod in solution and in the solid state by using the shortest structural unit of an “armchair” carbon nanotube (CNT), cycloparaphenylene (CPP), has been studied. [10]CPP and [11]CPP exothermically formed 1:1 complexes with...

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Bibliographic Details
Published in:Chemistry : a European journal 2013-10, Vol.19 (42), p.14061-14068
Main Authors: Iwamoto, Takahiro, Watanabe, Yoshiki, Takaya, Hikaru, Haino, Takeharu, Yasuda, Nobuhiro, Yamago, Shigeru
Format: Article
Language:English
Subjects:
Chemistry
encapsulation
fullerenes
host-guest systems
Nanotubes
supramolecular chemistry
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Summary:The size‐ and orientation‐selective formation of the shortest‐possible C70 peapod in solution and in the solid state by using the shortest structural unit of an “armchair” carbon nanotube (CNT), cycloparaphenylene (CPP), has been studied. [10]CPP and [11]CPP exothermically formed 1:1 complexes with C70, thereby giving the resulting peapods. A van′t Hoff plot analysis revealed that the formation of these complexes in 1,2‐dichlorobenzene was mainly driven by entropy, whereas the theoretical calculations suggested that the formation of the complex in the gas phase was predominantly driven by enthalpy. C70 was found to exist in two distinct orientations inside the CPP cavity, namely “lying” and “standing”, depending on the specific size of the CPP. The theoretical calculations and the X‐ray crystallographic analysis revealed that the interactions between [10]CPP and the short axis of C70 in its lying orientation were isotropic and similar to those observed between [10]CPP and C60. However, the interactions between [11]CPP and C70 in its standing orientation were anisotropic, thereby involving the radial deformation of [11]CPP into an ellipsoidal shape. This “induced fit” maximized the van der Waals interactions with the long axis of C70. Theoretical calculations revealed that the deformation occurred readily with low energy loss, thus suggesting that CPPs are highly radially elastic molecules. These results also indicate that the same type of radial deformation should occur in CNT peapods that encapsulate anisotropic fullerenes. Like two peas: Cycloparaphenylene (CPP), the shortest structural unit in “armchair” carbon nanotubes, encapsulated C70 to form the shortest C70 peapods. C70 adopted “lying” and “standing” orientations in the cavity, depending on the size of the CPP.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201302694