Tetsuya Shishido

Preparation and Photophysical and Photoelectrochemical Properties of a Covalently Fixed Porphyrin–Chemically Converted Graphene Composite

Chemically converted graphene (CCG) covalently linked with porphyrins has been prepared by a Suzuki coupling reaction between iodophenyl-functionalized CCG and porphyrin boronic ester. The covalently linked CCG-porphyrin composite was designed to possess a short, rigid phenylene spacer between the porphyrin and the CCG. The composite material formed stable dispersions in DMF and the structure was characterized by spectroscopic, thermal, and microscopic measurements. In steady-state photoluminescence spectra, the emission from the porphyrin linked to the CCG was quenched strongly relative to that of the porphyrin reference. Fluorescence lifetime and femtosecond transient absorption measurements of the porphyrin-linked CCG revealed a short-lived porphyrin singlet excited state (38 ps) without yielding the porphyrin radical cation, thereby substantiating the occurrence of energy transfer from the porphyrin excited state to the CCG and subsequent rapid decay of the CCG excited state to the ground state. Consistently, the photocurrent action spectrum of a photoelectrochemical device with a SnO(2) electrode coated with the porphyrin-linked CCG exhibited no photocurrent response from the porphyrin absorption. The results obtained here provide deep insight into the interaction between graphenes and π-conjugated systems in the excited and ground states.

Photophysics and photoelectrochemical properties of nanohybrids consisting of fullerene-encapsulated single-walled carbon nanotubes and poly(3-hexylthiophene)

Novel nanohybrids of single-walled carbon nanotubes (SWNTs) encapsulating C60 or C70 with poly(3-hexylthiophene) (P3HT) have been prepared and their photophysics and photoelectrochemical properties are studied in detail for the first time. Strong π–π interaction between the SWNT sidewalls and P3HT afforded successful dissolution of the so-called fullerene peapods into an organic solvent, as in the case of empty SWNTs (p-SWNTs). Fluorescence emission of P3HT in the SWNT–P3HT hybrids was completely quenched by the SWNTs regardless of the fullerenes insertion. Transient absorption and fluorescence up-conversion techniques revealed the excited state dynamics of the nanohybrids, where exciplex formation from the short-lived P3HT singlet excited state (∼0.2 ps) with the fullerene peapods and subsequent relaxation to the ground state within ∼1 ps occurred dominantly. Significant difference in the photodynamics upon encapsulation of C60 or C70 was not detected, implying little participation of the fullerenes in the excited state event and thus the inability of the encapsulated fullerenes to generate the charge-separated state between the fullerene peapods and P3HT. Photoelectrochemical devices based on the peapod–P3HT nanohybrids showed almost the same incident photon-to-current efficiencies as those for the p-SWNT–P3HT-based device, which is in good agreement with the results of the time-resolved spectroscopies. Thus, the results obtained here will give a deep insight into the photophysics and photoelectrochemical properties of fullerene peapod–conjugated polymer as well as SWNT–conjugated polymer hybrids and therefore provide valuable information on the design of peapod-based optoelectronic devices.

Carbon nanotube wiring of donor-acceptor nanograins by self-assembly and efficient charge transport.

Grain wiring: Functionalized single-wall carbon nanotube wiring between the nanograins of porphyrin (donor)-C60 (acceptor) dyads results in efficient charge transport between them, leading to the highest incident photon-to-current efficiency (22 %) ever reported for analogous photoelectrochemical devices utilizing donor-acceptor linked dyads.

Intermolecular [2+2+1] Carbonylative Cycloaddition of Aldehydes with Alkynes, and Subsequent Oxidation to γ‐Hydroxybutenolides by a Supported Ruthenium Catalyst

Intermolecular [2+2+1] carbonylative cycloaddition of aldehydes with alkynes and subsequent oxidation to γ-hydroxybutenolides is achieved using a supported ruthenium catalyst. A ceria-supported ruthenium catalyst promotes the reaction efficiently, even with an ambient pressure of CO or without external CO, thus giving the corresponding γ-hydroxybutenolide derivatives in good to high yields. Moreover this catalyst can be reused with no loss of activity.

Effects of reaction temperature on the photocatalytic activity of photo-SCR of NO with NH3 over a TiO2 photocatalyst

Effects of reaction temperature on the activity of photo-assisted selective catalytic reduction (photo-SCR) of NO with NH3 were investigated under very high GHSV conditions (100 000 h−1). The reaction temperature had a significant effect on the photo-SCR activity over a TiO2 photocatalyst. Maximum NO conversion was achieved at 433 K (NO conversion = 84%, N2 selectivity = 100%). The apparent activation energies in the low and high temperature range were evaluated to be 9.0 kJ mol−1 (353–433 K) and −2.7 kJ mol−1 (493–593 K), respectively. Kinetic analysis revealed that the rate-determining step in the photo-SCR was decomposition of NH2NO intermediates in all the ranges of the reaction temperature (353–593 K). The reaction temperature affects not only the rate constant of decomposition of NH2NO intermediates but also the total number of active sites ([S]0) and the equilibrium constant of NH3 adsorption, resulting in the dynamic change in the reaction rate.

Reaction Mechanism and the Role of Copper in the Photooxidation of Alcohol over Cu/Nb2O5

Loading of a small amount of copper on Nb(2)O(5) significantly enhances the activity of alcohol photooxidation without organic solvents. Alcohol is adsorbed on the Lewis acid site (Nb(V)) to form an alkoxide species. Photogenerated holes and electrons on Cu/Nb(2)O(5) are trapped by the adsorbed alkoxide and Cu(II) species to form the alkoxide carbon radical and Cu(I) species. The formed alkoxide carbon radical is converted to a carbonyl compound and then desorbed. Finally, the reduced Cu(I) sites are reoxidized by reaction with O(2). The alcohol photooxidation over Nb(2)O(5) takes place under not only UV irradiation but also under visible light irradiation up to 450 nm, although the band gap of Nb(2)O(5) is 390 nm (3.2 eV). DFT calculations reveal that 1) the surface donor level derived from the adsorbed alkoxide species is located in the forbidden band, 2) direct electron transition from the surface donor level to the conduction band takes place by absorbing a photon, 3) the excitation energy from surface donor level to the Nb 4d conduction band is lower than that from the O 2p valence band to Nb 4d. The kinetic study and FT/IR spectra suggest that Cu(I) acts as an effective desorption site for the products. Based on these results, we conclude that copper functions as an effective redox promoter and desorption site for the product.

Visible-light-assisted selective catalytic reduction of NO with NH[3] on porphyrin derivative-modified TiO[2] photocatalysts

Porphyrin-derivative-modified TiO2 photocatalysts showed high photocatalytic activity for the selective catalytic reduction of NO with NH3 in the presence of O2 under visible-light irradiation. Tetra(p-carboxyphenyl)porphyrin (TCPP) was the most effective photosensitizer among the five porphyrin derivatives investigated. NO conversion and N2 selectivity of 79.0% and 100%, respectively, were achieved at a gas hourly space velocity of 50 000 h−1. UV–Vis and photoluminescence spectroscopies revealed the presence of two species of TCPP on the TiO2 surface; one was a TCPP monomer and the other was an H-aggregate of the TCPP molecules. It was concluded that the TCPP monomer is an active species for the photo-assisted selective catalytic reduction (photo-SCR). Moreover, an increase in the fraction of H-aggregates with increasing TCPP loading amount resulted in a decrease in the photocatalytic activity of the photo-SCR.

Local Structure and La L1 and L3-Edge XANES Spectra of Lanthanum Complex Oxides

La L1 and L3-edge X-ray absorption near-edge structure (XANES) of various La oxides were classified according to the local configuration of La. We found a correlation between both of the areas of the pre-edge peaks of the La L1-edge XANES spectra and the full width at half-maximum of white line of La L3-edge XANES spectra and the local configuration of La. Theoretical calculation of the XANES spectra and local density of states reveals the difference of La L1 and L3-edge XANES spectra of various La compounds is related to the p-d hybridization of the unoccupied band and broadening of the d band of La induced by the difference of local configuration. In addition, simplified bond angle analysis parameters defined by the angles of the La atom and the two adjacent oxygen atoms are correlated to the pre-edge peak intensity of the La L1-edge XANES spectra. These results indicate that quantitative analysis of La L1 and L3-edge XANES spectra could be an indicator of the local structure of La materials.

Synthesis of low bandgap polymers based on thienoquinodimethane units and their applications in bulk heterojunction solar cells

A non-fused ring building block of an electron-rich quinoid structure, 2,5-thienoquinodimethane, has been synthesized and used in the synthesis of novel donor (D)–acceptor (A) type low bandgap polymers for the first time. Namely, 2,5-thienoquinodimethane with 4-(tert-butyl)phenyl or 4-(octyloxy)phenyl side chain as a solubilizing group was copolymerized with an electron-deficient diketopyrrolopyrrole subunit (PQD1 and PQD2, respectively). These polymer films exhibited broad and intense absorption bands in the region of 400–1000 nm. Photovoltaic devices with active layers consisting of PQD1 or PQD2 with [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM) revealed a broad photoresponse range covering from 400 to 1000 nm, whereas the power conversion efficiencies (η) were found to be moderate (1.44% for PQD1 and 0.96% for PQD2) under the illumination of AM 1.5G, 100 mW cm−2. The superior η value of the PQD1:[70]PCBM-based device relative to the PQD2:[70]PCBM-based device can be attributed to the more favorable phase separation nanostructure in the active layer as well as the higher crystallinity of PQD1 than PQD2. These results provide valuable, basic guidelines for rational designs of quinoidal heterole-based low bandgap polymers for high performance organic solar cells.

In situ time-resolved DXAFS study of Rh nanoparticle formation mechanism in ethylene glycol at elevated temperature

A combination of in situ time-resolved DXAFS and ICP-MS techniques reveals that the formation process of Rh nanoparticles (NPs) from rhodium trichloride trihydrate (RhCl(3)·3H(2)O) in ethylene glycol with polyvinylpyrrolidone (PVP) at elevated temperature is a first-order reaction, which indicates that uniform size Rh NPs appear consecutively and these Rh NPs do not aggregate with each other.