Anisotropic high electron mobility and photodynamics of a self-assembled porphyrin nanotube including C60 molecules

Hirofumi Nobukuni, Fumito Tani, Yuichi Shimazaki, Yoshinori Naruta, Kei Ohkubo, Tatsuaki Nakanishi, Takahiko Kojima, Shunichi Fukuzumi, Shu Seki

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A cyclic porphyrin dimer (Ni2-CPDPy) linked by butadiyne moieties bearing 4-pyridyl groups includes a C60 molecule inside its cavity in solution to give a 1:1 inclusion complex (C 60⊂Ni2-CPDPy). The charge-transfer (CT) band is observed at 645 nm in the UV-vis absorption spectrum of the solution of C60⊂Ni2-CPDPy. In the cyclic voltammogram of C60⊂Ni2-CPDPy, a small anodic shift of the porphyrin oxidation potential and a small cathodic shift of the fullerene reduction potential compared with their original redox potentials are indicative of CT interaction from the porphyrin to C60. In the crystal structure of C60⊂Ni2-CPDPy, a porphyrin nanotube is formed by the self-assembly of Ni2-CPDPy. Ni2-CPDPy molecules link together through nonclassical C-H· · ·N hydrogen bonds and π-π interactions of the pyridyl groups along the crystallographic b axis. The included C60 molecules are linearly arranged in the nanotube to afford a supramolecular peapod. The charge-carrier mobility of the single crystal of C 60⊂Ni2-CPDPy was determined by flash-photolysis timeresolved microwave conductivity (FP-TRMC) measurements. It has an anisotropic high electron mobility (Σμ ) 0.72 cm2 V-1 s-1) along the linear array of C60 (crystallographic b axis). Femtosecond laser flash photolysis of C 60⊂Ni2-CPDPy in the solid state with photoexcitation at the Soret band of the porphyrin shows the formation of a triplet exciplex 3{Ni2-CPDPy · · ·C60}*, which decays with a lifetime of 34 ps to the ground state without observation of a complete charge-separated state.

Original languageEnglish
Pages (from-to)19694-19699
Number of pages6
JournalJournal of Physical Chemistry C
Issue number45
StatePublished - 2009


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