Exciplex Intermediates in Photoinduced Electron Transfer of Porphyrin−Fullerene Dyads

Kesti, Tero; Tkachenko, Nikolai V.; Vehmanen, Visa; Yamada, Hiroko; Imahori, Hiroshi; Fukuzumi, Shunichi; Lemmetyinen, Helge

doi:10.1021/ja0257772

Cited by 151 publications

(142 citation statements)

References 63 publications

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“…[29][30][31][32] Deceleration effect of higher fullerene, i.e., C 70 , for CR was also observed for porphyrin-C 70 dyad vs porphyrin-C 60 dyad with the same spacer. 55,84 On the basis of the experimental results, we proposed, for the first time, that of fullerenes are much smaller than those of typical two-dimensional acceptors. 51 The photoinduced CS process in the Marcus normal region becomes fast with decreasing the value, whereas the CR process in the Marcus inverted region becomes slow with decreasing the value.…”

Section: Introductionmentioning

confidence: 90%

Creation of Fullerene-Based Artificial Photosynthetic Systems

Imahori¹

2007

Bulletin of the Chemical Society of Japan

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156

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Various porphyrin-fullerene-linked systems have been prepared to elucidate the intrinsic electron-transfer properties of fullerenes. Photodynamical studies on porphyrin-fullerene-linked systems showed that spherical fullerenes accelerated photoinduced electron transfer and charge-shift, but slowed down charge recombination, which is in sharp contrast with those of conventional planar acceptors such as quinones and imides. For the first time, it was shown that the unique electron-transfer properties result from the small reorganization energies of fullerenes arising from the delocalized system on the sphere together with the rigid structure. The small reorganization energies make it possible to produce a long-lived charge-separated state with a high quantum yield in donor-fullerene systems. The finding also will allow us to construct light energy conversion systems as well as artificial photosynthetic models. Highly efficient photoinduced energy and electron transfer were achieved on gold and ITO electrodes modified with self-assembled monolayers of the porphyrin-fullerene-linked systems. We also developed dye-sensitized bulk heterojunction solar cell possessing both characteristics of dye-sensitized and bulk heterojunction solar cells. These results showed the advantages of fullerenes as electron acceptors in artificial photosynthetic model, photonic molecular devices and machines, and organic molecular electronics including solar cells.

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Section: Introductionmentioning

confidence: 90%

Creation of Fullerene-Based Artificial Photosynthetic Systems

Imahori¹

2007

Bulletin of the Chemical Society of Japan

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156

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“…[36,37] We have reported that in a similar zinc porphyrin± C 60 system a charge-separated state is formed via an exciplex in polar solvents, whereas in a similar free-base porphyrin±C 60 system only the charge-separated state is produced in polar solvents. [38,39] Based on these results, two different mechanisms were proposed for the photocurrent generation in self-assembled monolayers of porphyrin±C 60 devices. The low quantum yield of the formation of a charge-separated state in the Au/1/MV 2+ /Pt device results in poor photocurrent generation, whereas the direct, efficient formation of a charge-separated state with a longer lifetime in the Au/2/MV 2+ /Pt device leads to a pronounced increase in the photocurrent generation.…”

Section: Introductionmentioning

confidence: 99%

“…The low quantum yield of the formation of a charge-separated state in the Au/1/MV 2+ /Pt device results in poor photocurrent generation, whereas the direct, efficient formation of a charge-separated state with a longer lifetime in the Au/2/MV 2+ /Pt device leads to a pronounced increase in the photocurrent generation. [38,39] …”

Section: Introductionmentioning

confidence: 99%

Porphyrin‐ and Fullerene‐Based Molecular Photovoltaic Devices

Imahori

Fukuzumi

2004

Adv Funct Materials

462

276

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We have developed a novel strategy for the construction of molecular photovoltaic devices where the porphyrins and fullerenes employed as building blocks are organized into nanostructured artificial photosynthetic systems by self‐assembly processes. Highly efficient photosynthetic energy‐ and electron‐transfer processes take place at gold and indium tin oxide (ITO) electrodes modified with self‐assembled monolayers of porphyrin‐ or fullerene linked systems. Porphyrins and fullerenes have also been assembled step by step to make large and uniform clusters on nanostructured semiconductor electrodes, which exhibit a high power‐conversion efficiency of close to 1 %. These results will provide valuable information on the design of donor–acceptor‐type molecular assemblies that can be tailored to construct highly efficient photovoltaic devices.

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“…3) affords the longer CS lifetime as compared with other zinc chlorin-fullerene dyads with the longer spacers. [36][37][38][39][40] A deoxygenated PhCN solution containing ZnCh-C 60 gives rise upon a 388 nm laser pulse to a transient absorption maximum at 460 nm due to the singlet excited state of ZnCh. 36 The decay rate constant was determined as 1:0 Â 10 11 s À1 , which agrees with the value determined from the fluorescence lifetime measurements.…”

Section: -17mentioning

confidence: 99%

Bioinspired Electron-Transfer Systems and Applications

Fukuzumi¹

2006

Bulletin of the Chemical Society of Japan

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199

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Bioinspired electron-transfer systems including artificial photosynthesis and respiration are presented herein together with some of their applications. First, multi-step electron-transfer systems composed of electron donor-acceptor ensembles have been developed, mimicking functions of the photosynthetic reaction center. However, a significant amount of energy is lost during the multi-step electron-transfer processes. Then, as an alternative to conventional charge-separation functional molecular models based on multi-step long-range electron transfer within redox cascades, simple donor-acceptor dyads have been developed to attain a long-lived and high energy charge-separated state without significant loss of excitation energy, by fine control of the redox potentials and of the geometry of donor-acceptor dyads that have small reorganization energies of electron transfer. Such simple molecular dyads, capable of fast charge separation but extremely slow charge recombination, have significant advantages with regard to synthetic feasibility, providing a variety of applications including construction of organic solar cells and development of efficient photocatalytic systems for the solar energy conversion. An efficient four-electron reduction of dioxygen to water by oneelectron reductants such as ferrocene derivatives as well as by an NADH analog has also been achieved as a respiration model by using a cofacial dicobalt porphyrin that can form the -peroxo Co(III)-O 2 -Co(III) complex. The catalytic mechanism of the four-electron reduction of dioxygen has been clarified based on the detailed kinetic study and the detection of the intermediate.There has been considerable interest in the photosynthetic reaction center of purple bacteria ever since the three-dimensional X-ray crystal structures of reaction centers of Rhodobacter (Rb.) sphaeroides 1 and other purple bacteria including Rhodopseudomonas (Rh.) viridis 2 have been disclosed. The photoinduced electron-transfer processes occur in a membrane-bound protein, which contains a number of cofactors, including four bacteriochlorophylls (BChl). Of these, the central part in Fig. 1 is referred to as the special pair [(BChl) 2 ], while the other two bacteriochlorophylls (BChl) are referred to as ''accessory'' bacteriochlorophylls. There are also two bacteriopheophytins (BPhe), two ubiquinones (Q A and Q B ), and a nonheme iron atom (not shown in Fig. 1), which together with the special pair are organized in pseudo-C 2 symmetry forming two branches (A and B). Light-initiated charge separation occurs between the special pair [(BChl) 2 ] and the neighboring pigments, leading to a radical cation [(BChl) 2 þ ]. Despite the quasi-symmetrical arrangement of the cofactors, the electrons are transported unidirectionally along the A-branch of the reaction center, 4-6 which suggests that the symmetry-breaking specific interactions with the protein are fundamentally important. The electron-transfer process is found to occur very rapidly from the special pair toward the quinones to pro...

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Exciplex Intermediates in Photoinduced Electron Transfer of Porphyrin−Fullerene Dyads

Cited by 151 publications

References 63 publications

Creation of Fullerene-Based Artificial Photosynthetic Systems

Creation of Fullerene-Based Artificial Photosynthetic Systems

Porphyrin‐ and Fullerene‐Based Molecular Photovoltaic Devices

Bioinspired Electron-Transfer Systems and Applications

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