Finely designed arrangements and photoelectronic properties of supramolecular nanocarbons composed of fullerenes and cyclic porphyrin dimers

Abstract

We have studied the supramolecular structures and photoelectronic properties of inclusion complexes of cyclic porphyrin dimers (M₂-CPD_Py, M=Ni, 2H) and fullerenes (C₆₀, C₇₀, PCBM ([6,6]-phenyl-C₆₁-butyric acid methyl ester) and Li⁺@C₆₀). The porphyrin dimers have self-assembling 4-pyridyl groups at the meso positions and include fullerenes in their cavities with high affinities (K_assoc≈10⁵ M^-1). In crystals, C₆₀⊂Ni₂-CPD_Py and PCBM⊂Ni₂-CPD_Py give self-assembled porphyrin nanotubes containing the linear arrays of fullerene molecules. These self-assemblies are induced mainly by the non-classical hydrogen bonds between pyridyl nitrogens and porphyin β C-H groups. On the other hand, in the crystals of C₆₀⊂H₄-CPD_Py and C₇₀⊂H₄-CPD_Py, the included fullerene molecules show zigzag chains through van der Waals contacts with each other. Due to these well-ordered arrays of C₆₀, both crystals of C₆₀⊂Ni₂-CPD_Py and C₆₀⊂H₄-CPD_Py have high charge mobilities (Σμ>0.1 cm² V^-1 s^-1). C₆₀⊂H₄-CPD_Py shows photoinduced electron transfer from the porphyrin moieties to C₆₀ and photovoltaic activity with IPCE_max=17% in photoelectrochemical cells. Moreover, the inclusion complexes of lithium-ion-encapsulated C₆₀(Li⁺@C₆₀) and M₂-CPD_Py exhibit photoinduced charge separation with very long lifetimes reaching submillisecond order.