The application of 58-π-1,4-bis(silylmethyl)[60]fullerenes, C₆₀(CH₂SiMe₂Ph)(CH₂SiMe₂Ar) (Ar=Ph and 2-methoxylphenyl for SIMEF-1 and SIMEF-2, respectively), in small-molecule organic solar cells with a diketopyrrolopyrrole donor (3,6-bis[5-(benzofuran-2-yl)thiophen-2-yl]-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione (DPP(TBFu)₂)) is demonstrated. With the 58-π-silylmethyl fullerene acceptor, SIMEF-1, the devices showed the highest efficiency of 4.57 % with an average of 4.10 %. They manifested an improved open-circuit voltage (1.03 V) owing to the high-lying LUMO level of SIMEF-1, while maintaining a high short-circuit density (9.91 mA cm⁻²) through controlling the crystallinity of DPP by thermal treatment. On the other hand, despite even higher open-circuit voltage (1.05 V), SIMEF-2-based devices showed lower performances of 3.53 %, owing to a low short-circuit current density (8.33 mA cm⁻²) and fill factor (0.40) arising from the asymmetric structure, which results in a lower mobility and immiscibility.

Reactions of 2,5-Bn₂C₇₀ (Bn=CH₂Ph) with hydroxide and ArCN (Ar=Ph, m-ClPh) followed by quenching with I₂ and BnBr afforded dibenzylated and tetrabenzylated oxazolino[70]fullerenes, respectively. The latter has a novel structural configuration, in which the addends are positioned from the polar to the transequatorial region. A key structural feature of this compound is that the oxygen atom of the oxazoline ring is bound to the equatorial belt region of C₇₀, giving structural change in its reduced state. This enables stabilization of the reduced state, suppressing charge recombination dynamics in organic solar cells to give a high open-circuit voltage (0.85, 0.93, and 1.11 V in devices using P3HT, PTB7, and DPP(TBFu)₂, respectively).

A 5,10-Bis(phenylethynyl)-15,20-bis(triisopropylsilylethynyl)porphyrin (cis-TIPSTEP) was synthesized by using phenylethynyl dipyrromethane and triisopropylsilylpropynal through scrambling of the ethynyl substituents. X-ray crystallographic structures of cis-TIPSTEP, 5-phenylethynyl-10,15,20-tris(triisopropylsilylethynyl)porphyrin, and 5,10,15,20-tetrakis(triisopropylsilylethynyl)porphyrin were determined in order to study the packing structure; cis-TIPSTEP exhibited good π-overlap and parallel π-stacking structures. 5,10-Bis(phenylethynyl)-15,20-bis(triisopropylsilylethynyl)porphyrinato magnesium (II) (Mg-cis-TIPSTEP) was synthesized for the use in small molecule organic solar cells, which gave power conversion efficiency of 1.5% with short-circuit current density of 4.5 mA/cm², open-circuit voltage of 0.83 V, and fill factor of 0.39. Copyright © 2013 John Wiley & Sons, Ltd.

Lithium-ion-encapsulated [6,6]-phenyl-C₆₁-butyric acid methyl ester fullerene (Li⁺@PCBM) was utilized to construct supramolecules with sulfonated meso-tetraphenylporphyrins (MTPPS⁴⁻; M=Zn, H₂) in polar benzonitrile. The association constants were determined to be 1.8×10⁵ M⁻¹ for ZnTPPS⁴⁻/Li⁺@PCBM and 6.2×10⁴ M⁻¹ for H₂TPPS⁴⁻/Li⁺@PCBM. From the electrochemical analyses, the energies of the charge-separated (CS) states were estimated to be 0.69 eV for ZnTPPS⁴⁻/Li⁺@PCBM and 1.00 eV for H₂TPPS⁴⁻/Li⁺@PCBM. Upon photoexcitation of the porphyrin moieties of MTPPS⁴⁻/Li⁺@PCBM, photoinduced electron transfer occurred to produce the CS states. The lifetimes of the CS states were 560 μs for ZnTPPS⁴⁻/Li⁺@PCBM and 450 μs for H₂TPPS⁴⁻/Li⁺@PCBM. The spin states of the CS states were determined to be triplet by electron paramagnetic resonance spectroscopy measurements at 4 K. The reorganization energies (λ) and electronic coupling term (V) for back electron transfer (BET) were determined from the temperature dependence of k_BET to be λ=0.36 eV and V=8.5×10⁻³ cm⁻¹ for ZnTPPS⁴⁻/Li⁺@PCBM and λ=0.62 eV and V=7.9×10⁻³ cm⁻¹ for H₂TPPS⁴⁻/Li⁺@PCBM based on the Marcus theory of nonadiabatic electron transfer. Such small V values are the result of a small orbital interaction between the MTPPS⁴⁻ and Li⁺@PCBM moieties. These small V values and spin-forbidden charge recombination afford a long-lived CS state.

The efficient nucleophilic addition of aryl Grignard reagents (aryl=4-MeOC₆H₄, 4-Me₂NC₆H₄, Ph, 4-CF₃C₆H₄, and thienyl) to C₆₀ in the presence of DMSO produced 1,2-arylhydro[60]fullerenes after acid treatment. The reactions of the anions of these arylhydro[60]fullerenes with either dimethylphenylsilylmethyl iodide or dimethyl(2-isopropoxyphenyl)silylmethyl iodide yielded the target compounds, 1-aryl-4-silylmethyl[60]fullerenes. The properties and structures of these 1-aryl-4-silylmethyl[60]fullerenes (aryl=4-MeOC₆H₄, thienyl) were examined by electrochemical studies, X-ray crystallography, flash-photolysis time-resolved microwave-conductivity (FP-TRMC) measurements, and electron-mobility measurements by using a space-charge-limited current (SCLC) model. Organic photovoltaic devices with a polymer-based bulk heterojunction structure and small-molecule-based p–n and p–i–n heterojunction configurations were fabricated by using 1-aryl-4-silylmethyl[60]fullerenes as an electron acceptor. The most efficient device exhibited a power-conversion efficiency of 3.4 % (short-circuit current density: 8.1 mA/ cm², open-circuit voltage: 0.69 V, fill factor: 0.59).

We synthesized a new 56-π-electron fullerene derivative through a Diels–Alder cycloaddition of benzo[c]thiophene that featured a relatively low temperature, closer to stoichiometric use of the diene, and easy product purification. The 56-π-electron benzo[c]thiophene diadduct (BTCDA) has a LUMO energy level of 0.09 to 0.18 eV higher than that of 58-π-electron fullerenes, and therefore, the BTCDA-based organic photovoltaic device exhibited a higher open-circuit voltage and power-conversion efficiency (PCE). When used with a binary-donor system, including visible-light-harvesting tetrabenzoporphyrin (BP) and near-IR-harvesting titanyl phthalocyanine (TiOPc), the device had a PCE that was 1.5–3 times higher (2.8 %) than that for devices with BP or TiOPc alone because the binary-donor device can utilize light between λ=350 and 950 nm.

Dianions of dimetallic hexa(organo)[70]fullerene [(C₅R₅)₂Ru₂C₇₀Ar₆]²⁻ (R=H, Me; Ar=Ph, 4-MeC₆H₄, 4-tBuC₆H₄) react with benzylic bromide to yield the dibenzylated product dimetallic octa(organo)[70]fullerene (C₅R₅)₂Ru₂C₇₀Ar₆(CH₂Ar′)₂ (Ar′=Ph, 4-MeO₂CC₆H₄), where the benzylic groups are attached to the equatorial belt region of [70]fullerene; this region is generally considered to be rather unreactive. This unusual structure was unambiguously determined by X-ray crystallography. Theoretical studies on the electronic properties of the monoanionic intermediate indicated that the highest spin density resides on the two carbon atoms in the belt region; one of them then couples with a benzylic radical to yield the octa(organo)fullerene product after ionic substitution of the fullerene anion with a benzylic bromide. Electrochemical analysis of the hexa(organo) and octa(organo) ruthenium complexes suggests that the modification of the belt region does not affect the electronic communication between the two metal centers.

Three multifunctionalized organo[60]fullerene derivatives, C₆₀Ph₅(C₆H₄-^tBu-4)₅Me₂ (cyclophenacene, 1), C₆₀Ph₅(C₆H₄-^tBu-4)₅Me₂ (fused corannulene, 2), and C₆₀Ph₅(C₆H₄-^tBu-4)₃Me₂ (phenylene-bridged fused corannulene, 3) are synthesized by the reaction of C₆₀Ph₅Me with 4-tert-butylphenylcopper reagent in the presence of pyridine, followed by treatment with MeI. Compounds 1–3 undergo reduction in the range from −1.8 to −2.5 V versus Fc/Fc⁺ and exhibit photoluminescence behavior with fluorescent quantum yields of 18.5%, 2.5%, and 3.2% with fluorescent lifetimes of 67, 1.1, and 27 ns (1–3, respectively). Organic electroluminescent diode devices using 1–3 are fabricated with π-conjugated polymers and show external electroluminescent efficiencies of 0.04%, 0.07%, and 0.03% emitting yellow, green, and red light, respectively. The device containing all three compounds emits white light. This result indicates that the bulky addends in 1–3 can effectively isolate the π-conjugated systems of the molecules in the solid state and retard the intermolecular excited-state quenching process.

A new type of fullerene–pyrene hybrid molecule, C₆₀Ar₅R [Ar=1-pyrenyl, 4-(1-pyrenyl)C₆H₄, 4-{(1-pyrenyl)CO₂}C₆H₄, and 4-{(1-pyrenyl)(CH₂)₃CO₂}C₆H₄; R=H and Me] was synthesized by a regioselective penta-addition reaction using organocopper reagents. The compounds were investigated using electrochemical measurements, DFT calculations, single-crystal X-ray structural analysis, and spectroscopic and fluorescence measurements. Intramolecular and intermolecular fullerene–pyrene and pyrene–pyrene interactions were characterized in the crystals. Fluorescence measurements in dilute solutions suggested the presence of intramolecular fullerene–pyrene and pyrene–pyrene interactions.

New fullerene–ferrocene arrays, [Ru(C₆₀Me₅)(C₄H₆Fc)(CO)₂] (Fc=ferrocenyl) and [Ru(C₆₀Me₅)(CCFc)(CO)₂], in which the ruthenium complex functions as a conjugative bridge, were synthesized by the reaction of [Ru(C₆₀Me₅)Cl(CO)₂] with FcC₆H₄MgBr and FcCCLi, respectively. These compounds were investigated by electrochemical measurement, single-crystal X-ray structural analysis, and photophysical measurement. Upon photoirradiation, the former compound was converted rapidly into the corresponding triplet state in toluene (τ_singlet=21 ps), whereas the charge-separated state was predominant in THF (τ_singlet=10.5 ps; τ_CS=355 ps). The latter compound, on the other hand, formed the charge-separated state in both toluene and THF (τ_singlet=3.0 ps; τ_CS=152 ps). Thus, the structural difference between the phenylene and acetylene bridges in 1 and 2, respectively, was found to change the outcome of the photophysical processes.