Hiroshi Imahori

Recently, dye-sensitized solar cells have attracted much attention relevant to global environmental issues. Thus far, ruthenium(II) bipyridyl complexes have proven to be the most efficient TiO(2) sensitizers in dye-sensitized solar cells. However, a gradual increment in the highest power conversion efficiency has been recognized in the past decade. More importantly, considering that ruthenium is a rare metal, novel dyes without metal or using inexpensive metal are desirable for highly efficient

Abstract Redox‐active fullerenes can be covalently bound to a variety of donors, their photophysical properties have been investigated. Their photochemical processes. Including electron transfer and energy transfer, are varied, depending on the donor, linkage between the donor and C 60 , and solvent. Regardless of the solvent and linkage, the charge‐separated state is produced efficiently in zinc porphyrin‐C 60 systems, showing that C 6o is a good electron acceptor. The most intriguing character

Photoinduced charge separation (CS) and charge recombination (CR) processes have been examined in various porphyrin-fullerene linked systems (i.e., dyads and triads) by means of time-resolved transient absorption spectroscopy and fluorescence lifetime measurements. The investigated compounds comprise a homologous series of rigidly linked, linear donor-acceptor arrays with different donor-acceptor separations and diversified donor strength: freebase porphyrin-C60 dyad (H2P-C60), zincporphyrin-C60

An extremely long-lived charge-separated state has been achieved successfully using a ferrocene-zincporphyrin-freebaseporphyrin-fullerene tetrad which reveals a cascade of photoinduced energy transfer and multistep electron transfer within a molecule in frozen media as well as in solutions. The lifetime of the resulting charge-separated state (i.e., ferricenium ion-C(60) radical anion pair) in a frozen benzonitrile is determined as 0.38 s, which is more than one order of magnitude longer than an

Abstract 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 hav

Three different kinds of mixed self-assembled monolayers have been prepared to mimic photosynthetic energy and electron transfer on a gold surface. Pyrene and boron-dipyrrin were chosen as a light-harvesting model. The mixed self-assembled monolayers of pyrene (or boron-dipyrrin) and porphyrin (energy acceptor model) reveal photoinduced singlet-singlet energy transfer from the pyrene (or boron-dipyrrin) to the porphyrin on the gold surface. The boron-dipyrrin has also been combined with a reacti

Four different kinds of C60-linked zincporphyrins have been prepared by changing systematically the linking position at meso-phenyl ring from ortho to para and their photophysical properties have been investigated. Regardless of the linkage between the two chromophores, photoinduced charge separation (CS) and subsequent charge recombination (CR) were observed in a series of zincporphyrin-C60 dyads by picosecond fluorescence lifetime measurements and time-resolved transient absorption spectroscop

Synthetic giant multiporphyrin arrays with well-defined architectures are reviewed in terms of artificial light-harvesting materials. Meso,meso-linked porphyrin arrays and multiporphyrin dendrimers have successfully mimicked the light-harvesting function of bacterial photosynthetic systems. We have also developed novel multiporphyrin-modified metal nanoclusters where porphyrins employed as a light-harvesting unit are well organized onto metal nanoclusters by self-assembly processes. Multiporphyr

We have prepared a variety of porphyrin-fullerene linked systems to mimic photoinduced energy and electron transfer (ET) processes in photosynthesis. Photodynamical studies on porphyrin and analogs-fullerene linked systems have revealed the acceleration of photoinduced electron transfer and charge-shift and the deceleration of charge recombination, which is reasonably explained by the small reorganization energies of electron transfer in fullerenes. In this context, we have proposed two strategi

Both charge-transfer absorption and emission have been observed in porphyrin-linked fullerene where the C60 moiety is closely located on the porphyrin plane. Electron-transfer parameters including reorganization energies, free energy changes, and electronic coupling matrix elements were determined by analyzing the charge-transfer absorption and emission in benzene. The reorganization energy is estimated as 0.23 ± 0.11 eV, which is the smallest value among inter- and intramolecular donor−acceptor

Time resolved absorption spectroscopy has been used to study photoinduced electron injection and charge recombination in Zn-porphyrin sensitized nanostructured TiO(2) electrodes. The electron transfer dynamics is correlated to the performance of dye sensitized solar cells based on the same electrodes. We find that the dye/semiconductor binding can be described with a heterogeneous geometry where the Zn-porphyrin molecules are attached to the TiO(2) surface with a distribution of tilt angles. The

Over the last decades, porphyrin sensitizers have made a remarkable contribution to performance improvement in dye-sensitized solar cells (DSSCs). In particular, versatile push-pull-type porphyrin sensitizers have achieved power conversion efficiencies (η) over 10% as a result of their improved light-harvesting abilities. Meanwhile, aromatic ring fusion to a porphyrin core is an attractive option for highly efficient DSSCs because of its expanded π-conjugation and resultant red-shifted absorptio