Structurally Defined High-LUMO-Level 66π-[70]Fullerene Derivatives: Synthesis and Application in Organic Photovoltaic Cells

Two new reactions for the synthesis of structurally defined 66π-electron [70]­fullerene derivatives are reported. The first provides synthetic access to tetra-phenyl or [3 + 1] hybrid tetra-aryl C₇₀ adducts via oxidation of a fullerene copper complex [Ar₃C₇₀–Cu–Ar′]⁻ (Ar = Ph, 4-ⁿBuC₆H₄; Ar′ = Ph, 4-MeOC₆H₄). The second provides access to alkyl fullerene ethers, C₇₀Ar₃(2-EH) via AgClO₄-mediated coupling of a [70]­fullerene bromide C₇₀Ar₃Br with 2-ethylhexanol (2-EH). The first reaction afforded two types of regioisomers including a 3,10,22,25-adduct (denoted type I) and a 7,10,22,25-adduct (type II). The haptotropic migration of the copper on a cuprio fullerene intermediate was suggested to be responsible for the generation of the two regioisomers. The second reaction gave only one regioisomer (type II). The eight new 66π-electron [70]­fullerene derivatives synthesized are electrochemically and thermally stable, and their photoabsorption and electrochemical properties are closely related to the addition pattern. For example, the type II regioisomers have higher LUMO levels than the type I isomers. Through modification of the addends, the LUMO levels of these [70]­fullerene derivatives can be raised by as much as 220 meV, that is, from −3.80 to −3.58 eV. Solution-processed p-n junction organic photovoltaic devices using five soluble compounds <b>5</b>, <b>9</b>, <b>10</b>, <b>13</b>, and <b>15</b> as the n-type semiconducting materials were fabricated. The device using compound <b>15</b> (LUMO = −3.58 eV) showed the highest open circuit voltage (<i>V</i>_oc = 0.90 V) and a respectable PCE value of 3.33%. For <i>J</i>_sc and FF, type II compounds <b>10</b>, <b>13</b>, and <b>15</b> showed much higher values than did type I compounds <b>5</b> and <b>9</b>, suggesting that the type II addition pattern on C₇₀ may be superior to the type I pattern for efficient electron transport, likely because of better molecular packing in crystals as suggested by crystallographic data

Regioselective [2 + 2] Cycloaddition of a Fullerene Dimer with an Alkyne Triggered by Thermolysis of an Interfullerene C–C Bond

Heating of a singly bonded fullerene dimer in the presence of an alkyne forms a cyclobutene structure on only one of the two fullerene moieties, through a stereo- and regioselective [2 + 2] cycloaddition. Experimental and theoretical data suggest that the reaction is triggered by cleavage of the interfullerene C–C bond and formation of a monomeric fullerene radical

Regioselective [2 + 2] Cycloaddition of a Fullerene Dimer with an Alkyne Triggered by Thermolysis of an Interfullerene C–C Bond

Heating of a singly bonded fullerene dimer in the presence of an alkyne forms a cyclobutene structure on only one of the two fullerene moieties, through a stereo- and regioselective [2 + 2] cycloaddition. Experimental and theoretical data suggest that the reaction is triggered by cleavage of the interfullerene C–C bond and formation of a monomeric fullerene radical

Methanofullerenes, C₆₀(CH₂)_<i>n</i> (<i>n</i> = 1, 2, 3), as Building Blocks for High‑Performance Acceptors Used in Organic Solar Cells

Selective preparation of C₆₀(CH₂)_<i>n</i> (<i>n</i> = 1, 2, 3) was realized via a “Bingel-decarboxylation” route. A 54π-electron derivative of C₆₀(CH₂)₂, OQBMF, demonstrates an outstanding power conversion efficiency (PCE) of 6.43% (<i>V</i>_oc = 0.95 V, <i>J</i>_sc = 9.67 mA cm^–2, FF = 70%) in fullerene:P3HT solar cells since the small CH₂ addends lift up fullerene LUMO and increase <i>V</i>_oc significantly without decreasing mobility significantly

Synthesis and Photovoltaic Properties of Low Band Gap Polymers Containing Benzo[1,2-<i>b</i>:4,5-<i>c</i>′]dithiophene-4,8-dione

Synthesis and Photovoltaic Properties of Low Band Gap Polymers Containing Benzo[1,2-<i>b</i>:4,5-<i>c</i>′]dithiophene-4,8-dion