Masahiko Hashiguchi

Regioselective Synthesis of 1,4-Di(organo)[60]fullerenes through DMF-assisted Monoaddition of Silylmethyl Grignard Reagents and Subsequent Alkylation Reaction

Monoaddition of Grignard reagents, in particular tri(organo)silylmethylmagnesium chlorides, to [60]fullerene took place smoothly in the presence of dimethylformamide to produce (organo)(hydro)[60]fullerenes, C60R(1)H, in good yield (up to 93% isolated yield). The hydrofullerene was then deprotonated to generate the corresponding anion, C60R(-), which was then alkylated to obtain 58pi-electron di(organo)[60]fullerenes, C60R(1)R(2), in good to high yield (up to 93% overall yield). The two-step methodology provides a wide variety of 1,4-di(organo)[60] fullerenes bearing the same or different organic addends on the [60] fullerene core. By changing the addends, one can control the chemical and physical properties of the compounds at the molecular and bulk levels.

Penta(organo)[60]fullerenes as acceptors for organic photovoltaic cells

Pentaaryl[60]fullerene derivatives, C60(C6H4Ph)5Me, C60(C6H4OPh)5Me, C60(C6H4nBu)5Me, Fe[C60(C6H4nBu)5]Cp, and Ru[C60(C6H4nBu)5]Cp have been used as acceptor materials in bulk heterojunction-type organic photovoltaic cells in combination with poly(3-hexylthiophene) as a donor material. High open-circuit voltages (up to 0.76 V) were obtained, which are attributed to the high LUMO of the penta(organo)[60]fullerenes. Scanning electron microscopic analyses of the cross-section of the devices indicated a homogeneous distribution of the donor and the acceptor compounds, which accounts for the moderate short-circuit current and photocurrent conversion efficiency (η = 1.08).

FeCl3-Mediated Synthesis of Fullerenyl Esters as Low-LUMO Acceptors for Organic Photovoltaic Devices

C(60) reacted with aromatic and aliphatic carboxylic acids in the presence of inexpensive FeCl(3) at room temperature to produce hydroxyfullerenyl esters C(60)(OCOR)(OH) in up to 68% isolated yield. The hydroxyl group was utilized in functional group transformations to obtain a diester derivative C(60)(OCOAr)(OCOPh) (Ar = 2,6-xylyl) and a siloxyl derivative C(60)(OCOAr)(OSiMe(3)). The diester and siloxyl derivatives were found to possess low-lying LUMO levels were utilized in organic photovoltaic devices showing 1.3% power conversion efficiency.

Organic photovoltaics based on solution-processed benzoporphyrin

Organic photovoltaic cell is fabricated with tetrabenzoporhyrin (BP) as a donor material. Tetrabenzoporhyrin is formed by thermal conversion of the soluble precursor that has four bicycle rings instead of benzo-rings. Upon heat treatment above 150°C, the precursor molecule is converted to semiconductive benzoporphyrin, which is insoluble against conventional organic solvents. Hetero junction OPV cell is made of benzoporhyrin/fullerene layers with power conversion efficiency of 2.2%. Taking advantage of insoluble character of BP, p-i-n heterojunction OPV is successfully fabricated from solution, with BP/BP:fullerene/fullerene layers. This solution-processed p-i-n device exhibited further improvement of power conversion efficiency, 3.0%.

FeCl3-Mediated Retro-Reactions of Fullerene Derivatives to C60

Indene–C60 monoadduct (ICMA) and phenyl-C61-butyric acid methyl ester (PCBM) undergo retro-reactions in the presence of FeCl3 at 25°C for 1 hour, affording their parent fullerene C60. Substrate selectivity was found; the retro-reaction for methanofullerene (Bingel-reaction product) and pyrrolidinofullerene (Prato-reaction product) did not proceed at all to afford 100% recovery. The use of inexpensive FeCl3, mild reaction conditions, simple operations and substrate selectivity is advantageous and suggests several potential applications.