Photoconductivity of porphyrin nanochannels composed of diprotonated porphyrin dications with saddle distortion and electron donors

Tatsuaki Nakanishi, Takahiko Kojima, Kei Ohkubo, Taku Hasobe, Ken Ichi Nakayama, Shunichi Fukuzumi

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Supramolecular architecture named as porphyrin nanochannels (PNCs), including tetrathiafulvalene (TTF) and p-aminophenol as electron-donating guests in the inner space, was prepared with the hydrochloride salt of dodecaphenylporphyrin ([H 4DPP]C1 2) by self-assembly based on intermolecular Π-Π interactions. The crystal structure of the TTF-included PNC (PNC-TTF) was determined by X-ray crystallography. Intermolecular Π-Π interaction was recognized among peripheral phenyl groups of the Porphyrin, mainly in the direction of the crystallographic c axis to form a column structure. Photoinduced electron transfer from the guest molecules to [3/4 DPP]C12 occurred to give the electron-transfer state involving cation radicals of the guest molecules and one-electron reduced [H 4DPP]C1 2, {[H 4DPP C1 2}-, via the Photoexcited singlet state of [H 4DPP]C1 2 in PNC. The reactions were examined by solid-state femtosecond laser flash photolysis and ESR measurements to determine the rate constants of electron transfer and electronic structures of the cation radicals included in the cavity, respectively. A single crystal (0.87 × 0.23 × 0.10 mm 3) of PNC-TTF exhibited photoconductivity upon photoirradiation at 633 nm with a He-Ne laser (5 mW), and the photocurrent was 0.7 nA at electrical field strength of 3.5 × 10 4 V cm -1. The photocurrent showed direction dependence toward the crystallographic c axis. This indicates that the intermolecular Π-Π interaction is the main conduction pathway. Various PNC supramolecules including TTF and other electron-donating guest molecules were also employed to construct photoelectrochemical cells with use of SnO 2 transparent electrodes. Short-circuit photocurrent measurements were made on the cells with the OTE/SnO 2/PNC-guest photoanodes, and they exhibited clear photoresponse upon photoirradiation. The photocurrents increase with increasing the rate constants of the photoinduced electron transfer from the guest molecules to [H 4DPP]C1 2, exhibiting saturation behavior. The performance of the cell with the OTE/Sn0 2/PNC-TTF electrode exhibited the maximum IPCE (incident photon-to-current efficiency) value of 10.1% at 460 nm, which corresponded to the absorption maximum of the Soret band of [? 4DPP]C1 2 on the electrode.

Original languageEnglish
Pages (from-to)7492-7500
Number of pages9
JournalChemistry of Materials
Issue number24
StatePublished - 23 Dec 2008


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