Yuko Takao

Design of Fullerene Derivatives for Stabilizing LUMO Energy using Donor Groups Placed in Spatial Proximity to the C60 Cage

A series of arylated dihydrofullerene derivatives were synthesized to elucidate the effective design of fullerene derivatives for enhancing the performance of organic photovoltaics. The LUMO energy of the fullerenes was estimated by the first reduction potential and theoretical calculations. The results showed that the methoxy groups substituted at spatial proximity to the fullerene core offered significant stabilization of the LUMO level. The stabilizing effect of the directly arylated fullerenes is more significant than that of conventional methanofullerenes. The theoretical investigation was performed with regard to the electronic interaction between the methoxy and fullerene moieties.

Controlling the Polarity of Fullerene Derivatives to Optimize Nanomorphology in Blend Films

Developing a design strategy to establish the compatibility of acceptor materials with donor materials is important for the rational development of organic solar cells. We synthesized 2,6-dimethoxyphenyl methanofullerene derivatives to realize an enhanced open-circuit voltage, and we investigated polarities and their effects on the film morphology of the active layer. The polarities of the synthesized fullerene derivatives were affected significantly by the presence of functional groups, such as methoxy, ether, and ester groups. Macro/nanoscopic morphological investigation and spectroscopic analysis of the blend films of the poly(3-hexylthiophene)(P3HT)/fullerene derivatives showed that a balanced polarity between materials results in the formation of optimized nanomorphology without grains and robust phase separation. Measurements of the device performance of the photovoltaic cells composed of P3HT and the fullerene derivatives confirmed the same tendency as that shown in the morphological analysis. This finding enables us to obtain an improved power conversion efficiency because of the enhanced open circuit voltage derived from the fullerene derivatives.

Synthesis of thienyl analogues of PCBM and investigation of morphology of mixtures in P3HT

Summary Novel [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) analogues containing benzo[b]thiophene (3a, 3b) and thieno[3,2-b]thiophene (3c, 3d) were synthesized and characterized. The morphology of the thin films prepared from the mixtures of these methanofullerenes with regioregular poly(3-hexylthiophene) (P3HT) was investigated by AFM measurement and UV-Vis absorption spectroscopy. A solubility test of these methanofullerenes was performed by using dichloromethane as a solvent. es-TThCBM (3d) exhibited 1.4 times greater solubility in dichloromethane than PCBM.

Photooxidation of phenol derivatives using μ-(dihydroxo)dipalladium(II) bisporphyrin complex

μ-(dihydroxo)dipalladium(II) complex with N21, N22-etheno bridged tetraphenylporphyrin ligand was employed in the catalytic photooxidation of phenol derivative in aerated homogeneous solution with visible light irradiation. The Pd complex promoted the degradation of p-tert-butylphenol as well as Cu phthalocyanine under basic conditions and it worked as a photosensitizer even in neutral conditions in contrast with Cu phthalocyanine. Some phenol derivatives afforded corresponding quinones selectively in this photooxidation. The present Pd complex coordinated by the bidentate porphyrin ligand showed higher photosensitizing ability than tetraphenylporphyrin free-base and ordinary tetradentate tetraphenylporphyrin palladium(II) complex for photooxidation of 2,6-di-tert-butylphenol. This bidentate Pd complex showed higher light durability even under the conditions where photodegradation of porphyrin free-base and tetradentate Pd porphyrin were observed by extensive irradiation.

Properties and reactions of μ-(dihydroxo)dipalladium(II) bisporphyrin complexes

μ-(dihydroxo)dipalladium(II) bisporphyrin was obtained by the reaction of dicationic bis(aqua)Pd(II) complexes of N21, N22-bridged porphyrin with NaOH or triethylamine. The reaction gives a mixture of two isomers and caused deprotonation from the active methylene compounds to give organopalladium(II) porphyrin complexes under neutral conditions.

Preparation of copper complexes coordinated by N21,N22-etheno bridged porphyrin and the application to photooxidation of phenol derivatives

Copper(I) complexes coordinated with a N21,N22-etheno bridged porphyrin ligand were synthesized as a unique coordination structure. The copper porphyrin complexes promoted photooxidations of a phenol derivative in organic solution under aerobic condition with visible photoirradiation. The complexes could be immobilized on silica gel as a support and the obtained copper porphyrin composites showed high ability as photocatalysts for heterogeneous photooxidation of a phenol derivative in aqueous solution. The composites could be easily recovered and re-used after the reaction. The structural study found that the active species contributing to the photooxidation reaction was the di(μ-hydroxo)dicopper(II) complex of N21,N22-etheno bridged porphyrin generated by oxidation of corresponding copper(I) complex in the reaction system under homogeneous and heterogeneous condition.