梅山 有和

Novel conjugated polymers incorporating thieno[3,4-c][1,2,5]-thiadiazole (TTD) and 2,1,3-benzothiadiazole (BT) were synthesized. The TTD-BT copolymers displayed broad absorption bands in visible-near-infrared regions with optical band gaps of 1.1-1.2 eV. The HOMO energy levels were lower than those of TTD-oligothiophene alternating copolymers due to the electron-deficient nature of the BT unit. The photovoltaic device consisting of the polymer and a fullerene derivative ([70]PCBM) showed power conversion efficiencies of 0.01-0.08% under simulated AM 1.5G irradiation of 100 mW cm(-2).

A series of alkoxycarbonyl-substituted dihydronaphthyl-based [60]fullerene bis-adduct derivatives (denoted as C2BA, C4BA, and C6BA with the alkyl chain of ethyl, n-butyl, and n-hexyl, respectively) have been synthesized to investigate the effects of alkyl chain length and substituent pattern of fullerene bis-adducts on the film structures and photovoltaic properties of bulk heterojunction polymer solar cells. The shorter alkyl chain length caused lower solubility of the fullerene bis-adducts (C6BA > C4BA > C2BA), thereby resulting in the increased separation difficulty of respective bis-adduct isomers. The device performance based on poly(3-hexylthiophene) (P3HT) and the fullerene bis-adduct regioisomer mixtures was enhanced by shortening the alkyl chain length. When using the regioisomerically separated fullerene bis-adducts, the devices based on trans-2 and a mixture of trans-4 and e of C4BA exhibited the highest power conversion efficiencies of ca. 2.4%, which are considerably higher than those of the C6BA counterparts (ca. 1.4%) and the C4BA regioisomer mixture (1.10%). The film morphologies as well as electron mobilities of the P3HT:bis-adduct blend films were found to affect the photovoltaic properties considerably. These results reveal that the alkyl chain length and substituent pattern of fullerene bis-adducts significantly influence the photovoltaic properties as well as the film structures of bulk heterojunction solar cells.

Carbon nanotubes (CNTs) have many interesting properties. In particular, their photohyperthermic effect by near-infrared (NIR) irradiation could be used to kill cancer cells, and could thus be applied in photohyperthermic therapy. However, the solubility of CNTs must be improved before they can be used in biological applications. As DNA is reported to disperse the CNTs in aqueous solution with p-p interactions, we hypothesis that immunostimulatory CpG DNA may also disperse the CNTs in aqueous solution. In this study, we used CpG DNA to disperse single-walled CNTs (SWCNTs) in aqueous solution, in order to combine photohyperthermic effect and immunoactivation together to achieve a more effective cancer therapy. As expected, CpG DNA effectively dispersed the SWCNTs in aqueous solution via the formation of SWCNT/CpG DNA complexes. Moreover, the immunoreactivity of the SWCNT/CpG DNA complexes was investigated. The results showed that intratumoral administration of the SWCNT/CpG DNA complexes in mice enhanced the production level of inflammatory cytokines in tumor tissues. Finally, we evaluated the antitumor effects of the SWCNT/CpG DNA complexes in tumor-bearing mice. The result indicated that intratumoral administration of the SWCNT/CpG DNA complexes combined with NIR irradiation was a more effective approach to prevent the proliferation of tumor growth. (C) 2014 Elsevier B. V. All rights reserved.

In order to analyze the crystal transformation from hexagonal PbI2 to CH3NH3PbI3 by the sequential (two-step) deposition process, perovskite CH3NH3PbI3 layers were deposited on flat and/or porous TiO2 layers. Although the narrower pores using small nanoparticles prohibited the effective transformation, the porous-TiO2 matrix was able to help the crystal transformation of PbI2 to CH3NH3PbI3 by sequential two-step deposition. The resulting PbI2 crystals in porous TiO2 electrodes did not deteriorate the photovoltaic effects. Moreover, it is confirmed that the porous TiO2 electrode had served the function of prohibiting short circuits between working and counter electrodes in perovskite solar cells. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

The polymer solar cell (PSC) technology has continued to be developed, and the power conversion efficiency (PCE) has now exceeded 10%. The rapid improvement of PCEs in the last decade has mainly resulted from versatile synthetic efforts for conjugated polymers as electron-donors and fullerene derivatives as electron-acceptors. This Feature Article highlights recent exploration of unique, attractive building blocks, i.e., quinoidal units, phospholes, porphyrins, and fluorinated aromatic rings, which can be incorporated into low bandgap conjugated polymers. As candidates for the next-generation acceptor materials that replace the benchmark acceptor, [6,6]-phenyl-C-61-butyric acid methyl ester ([60]PCBM), fullerene bisadduct regioisomers are also overviewed. Furthermore, we summarized recent attempts for the construction of one-dimensionally confined, organic donor-acceptor heterojunction nanorods and their applications to photovoltaic and optoelectronic devices. The topics in this article are not intended to cover an exhaustive list of PSC research studies, but involve the fundamental aspect to stimulate further studies for getting new insights into the structure-property relationship in PSC devices.

Two kinds of phosphole- and benzodithiophene-based copolymers bearing P-V=O or P-V=NSO2C8H17 functions were prepared by Pd-CuI-promoted Stille coupling reactions, and their optical and electrochemical properties were investigated. Bulk heterojunction organic photovoltaic devices comprised of the new P,S-bridged copolymers and (6,6)-phenyl-C71-butyric acid methyl ester (PC71BM) exhibited power conversion efficiencies of up to 0.65% under AM1.5 irradiation at 100 mWcm(-2).

Single-walled carbon nanotubes (SWCNTs) are known to have great potential for biomedical applications such as photothermal ablation of tumor cells in combination with near-infrared (NIR) irradiation. In this study, the photothermal activity of a novel SWCNTs composite with a designed peptide having a repeated structure of H-(-Lys-Phe-Lys-Ala-)(7)-OH [(KFKA)(7)] against tumor cells was evaluated in vitro and in vivo. The SWCNT-(KFKA)(7) composite demonstrated high aqueous dispersibility that enabled SWCNTs to be used in tumor ablation. The NIR irradiation of SWCNT-(KFKA)(7) solution resulted in a rapid temperature increase dependent on the SWCNTs concentration up to 50 mu g/ml. Three minutes of NIR irradiation of a colon 26 or HepG2 cell culture incubated with SWCNT-(KFKA)(7) resulted in remarkable cell damage, while that by single treatment with SWCNT-(KFKA)(7) or NIR irradiation alone was moderate. The intratumoral injection of SWCNT-(KFKA)(7) solution followed by NIR irradiation resulted in a rapid increase of the temperature to 43 degrees C in the subcutaneously inoculated colon 26 tumor based on thermographic observation and remarkable suppression of tumor growth compared with treatment with only SWCNT-(KFKA)(7) injection alone or NIR irradiation alone. These results suggest the a great potential of an SWCNT- peptide composite for use in photothermal cancer therapy. (C) 2013 Elsevier B.V. All rights reserved.

平成25年度 京都大学化学研究所 スーパーコンピュータシステム 利用報告書

To investigate the effect of fluorine substitution on molecular and film structures, optical, electrochemical, and photovoltaic properties of a moderate bandgap polymer, poly(2,7-carbazole-alt-dithienylbenzothiadiazole) (PCDTBT) with deep HOMO energy level, a fluorinated analogue of PCDTBT (i.e., PCDTBT-F) has been developed for the first time by replacing two hydrogen atoms on benzothiadiazole (BT) units with two fluorine atoms. An analogous polymer, PCBBBT-F with additional hexylthiophenes between the thiophene and carbazole of PCDTBT-F, has also been prepared to overcome the poor solubility of PCDTBT-F. The PCBBBT-F film showed wide absorption bands in UV and visible regions with an optical bandgap of 1.82 eV that is smaller than that of PCDTBT (1.89 eV), whereas the film of PCDTBT-F exhibited blue-shifted absorption with a bandgap of 1.96 eV due to the low molecular weight arising from the deficient solubility. The HOMO energy level of PCDTBT-F is lower than that of PCDTBT, owing to the electron-withdrawing fluorination of the BT unit, whereas PCBBBT-F exhibited a higher HOMO level than PCDTBT, implying that the additional incorporation of electron-donating hexylthiophenes negated the fluorination effect. A bulk heterojunction (BHJ) polymer solar cell (PSC) that employed PCDTBT-F or PCBBBT-F as an electron donor and a fullerene derivative [70]PCBM as an electron acceptor yielded lower power conversion efficiencies of 1.29 and 1.98%, respectively, than that of PCDTBT (6.16%) due to the unfavorable film structures of PCDTBT-F:[70]PCBM resulting from the poor solubility and low molecular weight, as well as low crystallinities and limited exciton lifetimes, of the fluorinated polymers. These results provide valuable information on the elaborate design of PCDTBT-based polymers for the PSC applications. © 2013 American Chemical Society.

Zero-, one-, and two-dimensional nanostructured carbon allotropes, i.e., fullerenes, single-walled carbon nanotubes (SWNTs), and graphenes, in combination with electron-donating conjugated molecules are promising building blocks for artificial photosynthesis and solar energy conversion. This feature article focuses on the fundamental aspects of covalently linked composites of porphyrins with fullerenes, SWNTs, and graphenes. The linkage structures between the porphyrin and nanocarbons have been found to exert a substantial impact on their interaction between the components in the ground and excited states. We also highlight recent developments of supramolecular nanocarbon hybrid materials of fullerenes and SWNTs, where SWNTs are utilized as scaffolds or wires of self-assembled fullerenes for photoelectrochemical devices and organic photovoltaics.

Functionalized chemically converted graphene (f-CCG) with high solubility has been incorporated into fullerene C-60 cluster and functionalized single-walled carbon nanotubes (f-SWNT)-fullerene C-70 hybrid cluster to form binary (i.e., graphene and fullerene) and ternary (i.e., graphene, fullerene, and carbon nanotubes) nanocarbon composites in solution processes for the first time. Electrophoretic deposition of the composites yielded the corresponding films on nanostructured SnO2 electrodes for photoelectrochemical devices. The device with the f-CCG-C-60 composites with an optimized weight ratio exhibited a higher incident photon-to-current efficiency (IPCE) value (6.0% at 400 nm) than that with the C-60 single-component cluster (5.1%). Electronic communication between C-60 clusters and f-CCG may facilitate the electron transport to the SnO2 electrode. However, the incorporation of f-CCG into f-SWNT-C-70 cluster made an adverse effect on photocurrent generation efficiencies because f-CCG inhibited formation of the porous network structure constructed by the f-SWNT-C-70 clusters. These results obtained here will provide valuable information on the design of optoelectronic devices composed of all-nanocarbon materials. (C) 2013 The Electrochemical Society. All rights reserved.

Quantum chemical methods are useful for materials design to improve the performance of organic bulk heterojunction (BHJ) solar cells. However, more integrated studies of quantum chemical modelling and experimental results need to be performed to further improve both the materials design and understanding of the related photo-induced processes and photocurrent generation. In this work we investigated the internal relationship between the molecular structures of four donor-acceptor (D-A) copolymers (P1-P4) and their photovoltaic performances. The effects of the molecular structures on the generation of photo-induced charge carriers, exciton diffusion, dissociation and carrier transmission were compared by combining density functional theory (DFT) calculations of intrinsic geometric, electronic and optical properties with the results of electrochemical, spectroscopic, thermal, AFM and solar cell measurements of the polymers. The quantum chemical methods, which provided a tool to assess the electronic properties and conjugation length in the polymers, highly support the experimental results and therefore the usefulness of quantum chemistry for solar cell materials design.

Recent progress of photoinduced artificial photosynthetic energy transfer systems is highlighted. Self-assembled multiporphyrin arrays as well as related energy transfer systems are found to be highly promising for efficient photocatalysts, organic solar cells, and molecular optoelectronic devices.

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-C-71-butyric acid methyl ester ([70]PCBM) revealed a broad photoresponse range covering from 400 to 1000 nm, whereas the power conversion efficiencies (eta) 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 eta 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.

Semiconducting and metallic single-walled carbon nanotubes (s-SWNTs and m-SWNTs) were enriched by agarose gel chromatography and their photothermal and photodynamic effects were compared in H2O. Under near-infrared laser irradiation, s-SWNTs generated reactive oxygen species (ROS) more than m-SWNTs, whereas m-SWNTs produced heat more efficiently than s-SWNTs. More importantly, cancer cell killing by PDE of s-SWNTs has been disclosed for the first time.

A novel composite material is developed with single-walled carbon nanotubes (SWCNTs) and artificially designed peptides, and its chemical and physicochemical characteristics are evaluated with an aim toward biomedical application. The peptides were designed to form a beta-sheet structure that would be suitable for wrapping SWCNTs. The complex of SWCNTs and peptide (SWCNTpeptide) showed good dispersibility in aqueous media and was considerably stable even in the absence of an excess amount of peptide in the media. The formation of SWCNTpeptide was confirmed by its performance in water, atomic force microscopy and transmission electron microscopy observation, and molecular modeling. The possibility of introducing various functions to SWCNTpeptide was also demonstrated by several methods, such as introduction of special amino acids, chemical modification, and additional complex formation based on electrostatic interaction. These results suggest the potential of the SWCNTpeptide complex as a molecular platform on which a desirable structure and/or function can be constructed for biomedical and industrial application. (c) 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 101:33983412, 2012

A novel donor Acceptor-conjugated polymer PBITT Consisting of isothianaphthene (ITN) dimer. donor unit and thiazolothiazole acceptor unit was synthesized by thermal conversion method. First, a soluble precursor polymer with an alternating main chain structure of bicyclo[2.2.2]octadiene (BCOD)-fused thiophene dimer and benzodithiophene (PPBITT) was synthesized by palladium(0)-catalyzed Stille coupling reaction. The BCOD moiety underwent the retro-Diels-Alder reaction by the thermal treatment of a red PPBITT film to afford a dark blue film of PBITT that was insoluble in any organic solvents. The optical bandgap of PBITT (1.3 eV) became significantly narrow compared with that of PPBITT (2.1 eV) due to the stabilized quinoid resonance structure of the PBITT main chain. The field-effect hole mobility (mu(h)), of PBITT was determined to be 2.2 x 10(-4) cm(2) V-1 s(-1) with on-off ratio (I-on/I-off) of 2.5 x 10(2), whereas the corresponding PPBITT-based device did not show any p- and 4-type response. Organic photovoltaic (OPV) devices were fabricated based on the bulk heterojunction film of the polymers and [6,6]-phenyl-C-61-butyric acid Methyl ester (PCBM). The device with the PBITT:PCBM film exhibited higher short-circuit current and lower open-circuit voltage than those of the PPBITT:PCBM-based device, resulting in the comparable power conversion efficiency (similar to 0.3%). These results obtained here will provide fundamental information on the design of thermally induced donor-acceptor alternating polymers for organic electronics.

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 CCGporphyrin 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 SnO2 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 p-conjugated systems in the excited and ground states.

A novel conjugated polymer based on cyclopenta[2,1-b:3,4-b']dithiophene and 1,3,4-thiadiazole with two electron-withdrawing imine (C=N) nitrogen atoms in a five-membered ring has been synthesized by the Stille coupling reaction. Optical band gap of the polymer estimated from the absorption edge was found to be 1.77 eV. The photovoltaic device consisting of the polymer and a fullerene derivative (PCBM) showed a power conversion efficiency of 1.06% under simulated AM 1.5G irradiation of 100 mW cm(-2).

Thermal conversion strategy has been utilized in the synthesis of a novel low bandgap polymer containing isothianaphthene (ITN) dimer structure and benzodithiophene (BDT) unit in the backbone (PBIBDT). First, a highly soluble precursor polymer with an alternating main chain structure of bicyclo-[2.2.2]octadiene-fused thiophene dimer and BDT (PPBIBDT) was synthesized by a palladium(0)-catalyzed Stille coupling reaction. Then, heating of the yellow PPBIBDT film spin-coated on a glass plate yielded a dark blue film of PBIBDT that was insoluble in any organic solvents. Thermogravimetric analysis of PPBIBDT showed 14% weight loss with an onset at 230 degrees C, corroborating the occurrence of the thermally induced retro-Diels-Alder reaction. The PBIBDT film showed red-shifted, broad absorption in the visible and near-infrared regions with a maximum at 706 nm compared to the precursor polymer PPBIBDT with an absorption peak at 445 nm. The introduction of an ITN dirtier unit in the backbone lowered the bandgap owing to the stabilized quinoid resonance structure. The field-effect hole mobility of PBIBDT was determined to be 1.1 x 10(-4) cm(2) V-1 s(-1) with an on-off ratio of 2.5 x 10(2), while the PPBIBDT-based device revealed no p- and n-type responses. Organic photovoltaic devices were fabricated based on the planar heterojunction structure of PBIBDT and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) and showed a power conversion efficiency of 0.07% under standard AM1.5 sunlight (100 mW cm(-2)). These results obtained here will provide fundamental information on the design of thermally induced low bandgap polymers for device applications.

Large pi-conjugated compounds are promising building blocks for organic thin-film electronics such as organic light-emitting diodes, organic field-effect transistors, and organic photovoltaics. Utilization of porphyrins and phthalocyanines for this purpose is highly fascinating because of their excellent electric, photophysical, and electrochemical properties as well as intense self-assembling abilities arising from pi-pi stacking interactions. This paper focuses on fundamental aspects of self-assembled structures that have been obtained from porphyrin and phthalocyanine building blocks and more complex composites for photoinduced charge separation and charge transport toward the potential applications to organic thin-film electronics.

The effects of fullerene bisadduct regioisomers on solar cell performance have been examined for the first time and the two substituent positions on C-60 have been found to have a large impact on the solar cell performance.

Liquid crystalline donor (i.e., phthalocyanine) was covalently linked to acceptor (i.e, fullerene) to achieve efficient charge-transport properties in a liquid crystalline phase. The columnar structure exhibited highly efficient ambipolar charge-transport character, demonstrating the potential utility of the strategy in organic electronics.

Theoretical investigations on single-walled carbon nanotubes (SWNTs) functionalized by Bingel reaction were conducted using finite-length models based on density functional theory. The electronic structures of the adduct with Type 1 configuration, where the circumferential C-C bonds in sidewall are reacted with a malonate anion, are largely retained after the functionalization owing to the sidewall opening at the C-C bond between the bridgehead carbons. In contrast, Type 2 configurations, where the axial C-C bonds are the reaction sites, cause significant change in the electronic structures. Taking into account the experimental results that the electronic properties of SWNTs are largely maintained, Type 1 configurations are formed selectively. In addition, calculations on energies of transition states, intermediates, and products suggest that Type 1 geometry is thermodynamically favorable but kinetically unfavorable compared to Type 2. This indicates the occurrence of isomerization from Type 2 to Type 1 after the Bingel reaction, attaining both of the preservation of electronic structure and the improvement of solubility with the high concentration of the addend group.

We have prepared a novel push-pull porphyrin with an electron-donating diarylamino group at the meso-position and an electron-withdrawing 4-carboxy-2,3,5,6-tetrafluorophenylethynyl anchoring group at the opposite meso-position to address the substitution effects of the electron-withdrawing fluorine atoms on photovoltaic properties for the first time. The fluoro-substituted porphyrin showed slightly improved light-harvesting properties when compared to the reference porphyrin in solution, due to the enhancement of charge-trapsfer character. The fluoro-substituted porphyrin-sensitized TiO2 cell exhibited a moderate power conversion efficiency of 4.6% but was lower than the corresponding Value (6.9%) of the reference porphyrin-sensitized TiO2 cell. The carboxylic group in the reference porphyrin binds to the TiO2 surface with bidentate coordination, leading to formation of the densely packed monolayer on the TiO2 surface, whereas both of the electron-withdrawing fluorine atoms and the carboxylic group of the fluoro-substituted porphyrin interact with the TiO2 surface, adopting relatively parallel orientation to the TiO2 surface with monodentate binding of the carboxylic acid to the TiO2, eventually yielding to the small surface coverage and low cell performance due to the fast charge recombination and small amount of the long-lived porphyrin radical cation. Such fundamental information may be useful for the molecular design of highly efficient dye-sensitized solar cells based on push-pull porphyrins.

A bottom-up strategy has been developed to construct a multiple electron transfer system composed of organic/inorganic ternary composites (porphyrin, zinc oxide nanoparticles, reduced graphene oxide) on a semiconducting electrode without impairing the respective donor-acceptor components. The hierarchical electron transfer cascade system exhibited remarkably high photo-current generation with an incident-photon-to-current efficiency of up to ca. 70%.

pi-A isotherms, ellipsometric measurements, Brewster angle microscopy (BAM) and reflection spectroscopy have been utilized to characterize the films of an amphiphilic porphyrin ((OD)(3)TPPS(3)) at the air-water interface as a function of pH. This porphyrin forms stable mono-molecular layers at such interfaces, and exhibits different J-aggregation as a function of pH. The J-aggregation of (OD)(3)TPPS(3) on neutral pH subphases is notable considering that the nitrogen atoms at the central macrocycle have a pK(a) approximate to 4.9. The type of aggregates at neutral pH is like those detected at pH <4, because the central porphyrin ring is already protonated. However at basic pH the aggregation happens without protonation of the central ring but can be instead controlled by application of the surface pressure. At the air-water interface, (OD)(3)TPPS(3) shows two bands, a red component and a blue component, which have characteristics of non-degenerate linear oscillators being perpendicularly polarized between each other. The spectral behavior observed on subphases at different pHs is qualitatively interpreted by means of exciton coupling theory, assuming that the degenerate transitions attributed to the Soret band are split. Additionally, highly oriented molecular films of these J-aggregates were deposited onto transparent quartz slides. (C) 2011 Elsevier Inc. All rights reserved.

Novel nanohybrids of single-walled carbon nanotubes (SWNTs) encapsulating C-60 or C-70 with poly(3-hexylthiophene) (P3HT) have been prepared and their photophysics and photoelectrochemical properties are studied in detail for the first time. Strong pi-pi 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 (similar to 0.2 ps) with the fullerene peapods and subsequent relaxation to the ground state within similar to 1 ps occurred dominantly. Significant difference in the photodynamics upon encapsulation of C-60 or C-70 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.

Solid-state nuclear magnetic resonance (NMR) has been applied to "amorphous" active layers consisting of donor-acceptor self-assembled composites in organic solar cells. Several stoichiometric supramolecular complexation states as well as the charge-transfer states are revealed by the solid-state NMR, which have been difficult to access by conventional spectroscopy. The spectra show clear correlation between local self-assembled supramolecular structures and the organic solar cell performances. (C) 2011 American Institute of Physics. [doi:10.1063/1.3565237]

5,10,15,20-Tetrakis(2,4,6-trimethylphenyl)-6'-carboxylquinoxalino[2,3-b]quinoxalino[12,13-b']porphyrinatozinc(II) (ZnPBQ) is synthesized to evaluate the effects of p elongation of quinoxaline-fused porphyrins on the optical, electrochemical, and photovoltaic properties. ZnPBQ showed an intensified Soret band as well as red-shifted Soret and Q bands relative to 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)-6'-carboxylquinoxalino[2,3-b] porphyrinatozinc(II) (ZnPQ), demonstrating the improved light-harvesting property of ZnPBQ. The optical and electrochemical HOMO-LUMO gaps were consistent with those estimated by DFT calculations. The photovoltaic properties were compared under optimized conditions, in which a sealed device structure with TiCl4-treated, TiO2 double layers was used. The ZnPBQ cell exhibited a relatively high power conversion efficiency (eta) of 4.7 %, which was smaller than that of the ZnPQ cell (eta = 6.3 %). The weaker electronic coupling between the LUMO of ZnPBQ and conduction band (CB) of TiO2 or more tilted geometry of ZnPBQ on the TiO2 surface may result in the low electron injection/charge collection efficiency as well as the low incident photon-to-current efficiency (IPCE) for the ZnPBQ cell (maximum IPCE = 56%) relative to the ZnPQ cell (maximum IPCE = 75 %), leading to the lower eta value of the ZnPBQ cell than that of the ZnPQ cell. In addition, the open-circuit potential of the ZnPBQ cell also slightly decreased with the effect of charge recombination from the electrons injected into the CB of TiO2 to I-3(-).

Fullerene-encapsulating single-walled carbon nanotubes (C-60@SWNT) linked with porphyrins by a short bridge have been prepared for the first time. Steady state and time-resolved spectroscopies demonstrated the initial formation of an exciplex state, followed by a charge-separated state.

A series of novel polythiophene derivatives comprised of alternating structures of N-alkylated thieno [3,4-c]pyrrole-4,6-dione (nTPD, n = number of carbon atoms from 11 to 18 in alkyl chains) and pristine thiophene were synthesized by Stille coupling reaction between 2,5-dibromo- or 2,5-diiodo-nTPD and 2,5-bis(tributylstannyl)thiophene. The effect of alkyl side-chain structures at the N-atom of TPD on the optical, electrochemical, and photovoltaic properties has been investigated systematically. In addition, these properties were compared with a widely used polythiophene derivative, i.e., poly(3-hexylthiophene) (P3HT). Optical bandgaps of the obtained polymers PnTPDTs estimated from absorption and fluorescence spectra were 1.8-2.1 eV, which were comparable or smaller than that of P3HT (2.0 eV). HOMO and LUMO energy levels of PnTPDTs were determined by electrochemical and optical measurements. The HOMO levels are -5.4 to -5.7 eV, which are lower than that of P3HT (-5.2 eV). The photovoltaic properties of the devices consisting of PnTPDT (n = 11, 12, 13, 18) with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) were investigated. The short-circuit currents (J(SC)) in the PnTPDT:PCBM devices were relatively low and varied significantly with alkyl side-chain structures (0.81-2.29 mA cm(-2)), whereas the open-circuit voltage (V(OC)) values were higher by 0.1-0.2 V than that in the P3HT:PCBM device. The P12TPDT:PCBM device exhibited the photocurrent generation exceeding wavelength of 750 nm, but the power conversion efficiency was found to be moderate (0.75%).

Single-walled carbon nanotube (SWCNT) thin films, containing a high-density of semiconducting nanotubes, were obtained by a gel-centrifugation method. The agarose gel concentration and centrifugation force were optimized to achieve high semiconducting and metallic nanotube separation efficiency at 0.1 wt% agarose gel and 18 000g. The thickness of SWCNT films can be precisely controlled from 65 to 260 nm with adjustable transparency. These SWCNT films were applied in photoelectrochemical devices. Photocurrents generated by semiconducting SWCNT enriched films are 15-35% higher than those by unsorted SWCNT films. This is because of reducing exciton recombination channels as a result of the removal of metallic nanotubes. Thinner films generate higher photocurrents because charge carriers have less chances going in metallic nanotubes for recombination, before they can reach electrodes. Developing more scalable and selective methods for high purity semiconducting SWCNTs is important to further improve the photocurrent generation efficiency by using SWCNT-based photoelectrochemical devices.

Good solvent effects of C-70 cluster formations and their electron-transporting and photoelectrochemical properties have been systematically examined for the first time Nano-to-micrometer scale assemblies of C-70 with different morphologies were prepared by rapidly injecting poor solvent (i e, acetonitrile) into a solution of C-70 dissolved in various good solvents (i e, benzene, toluene, chlorobenzene etc) The cluster morphology engineering was successfully achieved by changing the good solvent, yielding the spherical rodlike or platelike clusters in the mixed solvents The clusters of C-70 were electrophoretically deposited onto a nanostructured SnO2 electrode to examine the photoelectrochemical properties under the white light or monochromatic light illumination The maximum incident photon-to-current efficiency (IPCE) varied from 08 to 10% depending on the combinations of the poor-good solvents I he differences in the IPCE values are discussed in terms of the surface area thickness and electron mobility of the deposited cluster films I he electron mobility is found to be the most predominant factor for the IPCE indicating the importance of the election-transporting process in the overall photocurrent generation In addition the electron mobility is closely correlated with the underlying molecular alignment and the resultant cluster structure Thus these results will provide basic clue for the design of C-70-based molecular devices including the organic photovoltaics

We have prepared meso-bis(diarylamino)-substituted porphyrins (cis-ZnP and trans-ZnP), meso-diarylamino-substituted porphyrin (mono-ZnP), and porphyrin reference without the meso-diarylamino group (ZnP) to evaluate the effects of substituent number and position of the diarylamino groups on the optical, electrochemical, and photovoltaic properties of the porphyrins for the first time. With increasing the number of the diarylamino groups, the light-harvesting properties were improved in the visible region. The optical and electrochemical HOMO-LUMO gaps were parallel to those estimated by DFT calculations. The photovoltaic properties were compared under the optimized conditions in which a sealed device structure with TiCl4-treated, TiO2 double layers was used. The power conversion efficiency (eta) was in the order of the trans-ZnP (3.8%) < ZnP (4.4%) < cis-ZnP (5.5%) < mono-ZnP (6.5%) sensitized TiO2 cells. The low light-harvesting efficiency (LHE) rather than the high adsorbed photon-to-current efficiency (APCE) in the ZnP-sensitized solar cell leads to the moderate short circuit current (J(SC)), whereas both the high APCE value and the moderate LHE value in the mono-ZnP-sensitized TiO2 cell result in the highest J(SC) value. Considering the similarity in the LHE values of the trans-ZnP and cis-ZnP-sensitized cells, the APCE values correlate the J(SC) values. The open circuit potentials (V-OC) of the trans-ZnP and cis-ZnP-sensitized TiO2 cells are lower than those of the mono-ZnP and ZnP-sensitized TiO2 cells. Overall, the difference in the J(SC) and V-OC values of the four TiO2 cells leads to that in the eta values. The basic information obtained here will be useful to design molecular structures of porphyrins for highly efficient dye-sensitized solar cells.

An oligothiophene bearing 1-hydroxy-1-oxodithieno[2,3-b:3',2'-d]phosphole (TP) as a novel anchoring group has been synthesized for dye-sensitized solar cells (DSSC). Attenuated total reflectance-Fourier transform infrared and X-ray photoelectron spectroscopy measurements disclosed the bidentate binding of the phosphinic acid unit to a TiO2 surface. A TP-sensitized TiO2 cell yielded a maximum incident photon-to-current efficiency of 66% and a power conversion efficiency of 1.8%, indicating that 1-hydroxy-1-oxodithienophosphole is a potential unit as a new type of anchoring groups for DSSC.

For the first time nanocarbon composites with C(70) molecules aligned on the sidewall of single-walled carbon nanotubes (SWNTs) are demonstrated. The C(70)-SWNT photo-electrochemical devices exhibit efficient photocurrent generation properties that result from selective formation of a single composite film consisting of a SWNT network covered with C(70) molecules and high electron mobility through the C(70)-SWNT network.

The Cluster formation, electrophoretically deposited film Structures. microwave conductivity, and photoelectrochemical properties of the composites consisting of single-walled carbon nanotube (SWNT) with C-60, C-70, or C-84 have been systematically compared for the first time. In an ortho-dichlorobenzene (ODCB)-acetonitrile mixture, the higher fullerenes (i.e., CM and C-84) were found to form single composite Clusters exclusively with highly Soluble SWNT bearing bulk), swallow-tailed substituents (f-SWNT). These are in marked contrast with the unselective formation of three different clusters in the C-60-f-SWNT composites. Electrophoretic deposition of the composite clusters yielded the corresponding films on nanostructured SnO2 electrodes. The microwave conductivity measurements revealed the Occurrence of electron transfer from C-70 to f-SWNT, followed by electron transportation through f-SWNT, in addition to electron hopping through C-70 molecule arrays due to the alignment of C-70 on the sidewalls of f-SWNT in the C-70-f-SWNT film. The C-70-f-SWNT photoelectrochemical device exhibited higher incident photon-to-current efficiency (IPCE) value (26% at 400 nm) than the C-60-f-SWNT device (18%). The higher IPCE value results from selective formation of the single composite film, in which the SWNT network is covered with C-70 molecules, and the high electron mobility (2.4 cm(2) V-1 s(-1)) through the C-70-SWNT network. In contrast, the C-84-f-SWNT photoelectrochemical device revealed poor photocurrent generation (4.8%) owing to the inefficient electron injection from C-84 radical anion (C-84/C-84(center dot-) approximate to 0-0 V vs NHE) to the SnO2 electrode (E-CB = 0 V vs NHE) directly or indirectly despite the exclusive formation of the single composite clusters. Thus, the results obtained here will provide valuable information oil the design Of Molecular devices based on carbon nanotubes and fullerenes.