Synthesis, crystal structure, and photodynamics of π-Expanded Porphyrin-Fullerene dyads synthesized by Diels-Alder reaction

Hiroko Yamada, Kei Ohkubo, Daiki Kuzuhara, Tetsuro Takahashi, Atula S.D. Sandanayaka, Tetsuo Okujima, Keishi Ohara, Osamu Ito, Hidemitsu Uno, Noboru Ono, Shunichi Fukuzumi

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Free base and zinc porphyrins are linked with fullerene (C60) through β,β′-pyrrolic positions rather than meso-positions by Diels-Alder reaction of monoanthraporphyrins (H2P-mA and ZnP-mA) and C60 to afford a π-expanded free base porphyrin-fullerene dyad (H2P-C60) and its zinc porphyrin-fullerene dyad (ZnP-C60) in 86 and 51 % yield, respectively. The X-ray crystallographic analysis of ZnP-C60 showed two comma-shaped swirls-like structure in a unit cell. The intramolecular center-to-center and edge-to-edge distances between the porphyrin and fullerene moieties were 11.5 and 2.5 Å, respectively. The porphyrins and fullerenes were packed in layer-by-layer structure and the porphyrins lied down in parallel, The intermolecular center-to-center distances between the neighboring fullerenes were 10.252, 10.028, and 10.129 Å, which were less than typical van der Waals distance and the π-π interaction spread two-dimensionally. The energy of the charge-separated (CS) state of ZnP-C60 (1.11 eV) determined by differential-pulse voltammetry measurements in benzonitrile is significantly lower than those of zinc porphyrin-C60 dyads linked at meso positions because of the low oxidation potential of the <-expanded ZnP moiety. The CS energy of ZnP-C60 in a nonpolar solvent such as toluene (1.40 V) is lower than the triplet excited state of C60 (3C60*), enabling us to attain a longed lived triplet CS state (8.1 μs) in toluene, detected by nanosecond laser flash photolysis experiments. The distance between unpaired electrons in the triplet CS state was determined by the EPR spectrum to be 9.1 Å, which agreed with the distance between a zinc atom of the porphyrin and a carbon edge of C 60 in the crystal structure of ZnP-C60. The rate constants of photoinduced electron transfer and back electron transfer of H 2P-C60 and ZnP-C60, which were determined by femtosecond and nanosecond laser flash photolysis measurements, were analyzed in light of the Marcus theory of electron transfer.

Original languageEnglish
Pages (from-to)14717-14728
Number of pages12
JournalJournal of Physical Chemistry B
Issue number45
StatePublished - 8 Dec 2010


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