Shortest Double-Walled Carbon Nanotubes Composed of Cycloparaphenylenes

The host-guest chemistry of cycloparaphenylenes (CPPs) of different sizes is described. [n]CPPs (n= 5, 6, 7, 8, and 10) selectively interact with [n+5] CPPs, forming complexes [n+5] CPP superset of[n]CPP, which are the shortest double-walled armchair carbon nanotubes. The size selectivity is dictated by the difference in diameters of the CPPs (that is, 0.34-0.35 nm), which maximizes attractive van der Waals interactions. Theoretical calculations suggest that the orbital energies of the CPPs become perturbed upon complex formation, and orbital mixing between the two CPPs is predicted for large CPP pairs. The association constants in 1,1,2,2-[D-2] tetrachloroethane, estimated by H-1 NMR titration, are approximately 103 molL(- 1) at 508 degrees C. Van't Hoff plot analysis reveals that complexation is driven mainly by entropy owing to desolvation of the CPPs. [13] CPP also forms a complex with [4] cyclo-2,7-pyrenylene ([4] CPY), which is a p-extended [8]CPP. Theoretical calculations suggest that the formation of [13]CPP superset of [4]CPY is more exothermic than that of [13] CPP superset of[8]CPP. A ternary complex, [15] CPP superset of [10]CPP superset of C60, is also formed by mixing [15]CPP and [10]CPP superset of C60.