Hetero Bis-Addition of Spiro-Acetalized or Cyclohexanone Ring to 58π Fullerene Impacts Solubility and Mobility Balance in Polymer Solar Cells

Fullerene bis-adducts are increasingly being studied to gain a high open circuit voltage (<i>V</i>_oc) in bulk heterojunction organic photovoltaics (OPVs). We designed and synthesized homo and hetero bis-adduct [60]­fullerenes by combining fused cyclohexanone or a five-membered spiro-acetalized unit (SAF₅) with 1,2-dihydromethano (CH₂), indene, or [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). These new eight 56π fullerenes showed a rational rise of the lowest unoccupied molecular orbital (LUMO). We perform a systematic study on the electrochemical property, solubility, morphology, and space-charge-limited current (SCLC) mobility. The best power conversion efficiency (PCE) of 4.43% (average, 4.36%) with the <i>V</i>_oc of 0.80 V was obtained for poly­(3-hexylthiophene) (P3HT) blended with SAF₅/indene hetero bis-adduct, which is a marked advancement in PCE compared to the 0.9% of SAF₅ monoadduct. More importantly, we elucidate an important role of mobility balance between hole and electron that correlates with the device PCEs. Besides, an empirical equation to extrapolate the solubilities of hetero bis-adducts is proposed on the basis of those of counter monoadducts. Our work offers a guide to mitigate barriers for exploring a large number of hetero bis-adduct fullerenes for efficient OPVs

Facile and Exclusive Formation of Aziridinofullerenes by Acid-catalyzed Denitrogenation of Triazolinofullerenes

Variously substituted [6,6]closed aziridinofullerenes were exclusively obtained from acid-catalyzed denitrogenation of triazolinofullerenes without formation of relevant [5,6]open azafulleroids, which are the major products on noncatalyzed denitrogenation. The mechanistic consideration by DFT calculations suggested a reaction sequence involving initial pre-equilibrium protonation of the triazoline N₁ atom, generation of aminofullerenyl cation by nitrogen-extrusion, and final aziridination

Crystallographic information file of [Li+@C60](TFPB−)∙C4H10O at 260 K from Structure of [60]fullerene with mobile lithium cation inside

Crystallographic information file of [Li+@C60](TFPB−)∙C4H10O at 260

Crystallographic information file of [Li+@C60−](NiOEP)∙CH2Cl2 at 400 K from Structure of [60]fullerene with mobile lithium cation inside

Crystallographic information file of [Li+@C60−](NiOEP)∙CH2Cl2 at 400

Crystallographic information file of [Li+@C60](TFSI−)∙CH2Cl2 at 150 K from Structure of [60]fullerene with mobile lithium cation inside

Crystallographic information file of [Li+@C60](TFSI−)∙CH2Cl2 at 150

Stereochemistry of Spiro-Acetalized [60]Fullerenes: How the <i>Exo</i> and <i>Endo</i> Stereoisomers Influence Organic Solar Cell Performance

Exploiting bis-addition products of fullerenes is a rational way to improve the efficiency of bulk heterojunction-type organic photovoltaic cells (OPV); however, this design inherently produces regio- and stereoisomers that may impair the ultimate performance and fabrication reproducibility. Here, we report unprecedented <i>exo</i> and <i>endo</i> stereoisomers of the spiro-acetalized [60]­fullerene monoadduct with methyl- or phenyl-substituted 1,3-dioxane (<b>SAF</b>_<b>6</b>). Although there is no chiral carbon in either the reagent or the fullerene, equatorial (<i>eq</i>) rather than axial (<i>ax</i>) isomers are selectively produced at an <i>exo-eq</i>:<i>endo</i>-<i>eq</i> ratio of approximately 1:1 and can be easily separated using silica gel column chromatography. Nuclear Overhauser effect measurements identified the conformations of the straight <i>exo</i> isomer and bent <i>endo</i> isomer. We discuss the origin of stereoselectivity, the anomeric effect, intermolecular ordering in the film state, and the performance of poly­(3-hexylthiophene):substituted <b>SAF</b>_<b>6</b> OPV devices. Despite their identical optical and electrochemical properties, their solubilities and space-charge limited current mobilities are largely influenced by the stereoisomers, which leads to variation in the OPV efficiency. This study emphasizes the importance of fullerene stereochemistry for understanding the relationship between stereochemical structures and device output

Kinetic Study of the Diels–Alder Reaction of Li⁺@C₆₀ with Cyclohexadiene: Greatly Increased Reaction Rate by Encapsulated Li⁺

We studied the kinetics of the Diels–Alder reaction of Li⁺-encapsulated [60]­fullerene with 1,3-cyclohexadiene and characterized the obtained product, [Li⁺@C₆₀(C₆H₈)]­(PF₆^–). Compared with empty C₆₀, Li⁺@C₆₀ reacted 2400-fold faster at 303 K, a rate enhancement that corresponds to lowering the activation energy by 24.2 kJ mol^–1. The enhanced Diels–Alder reaction rate was well explained by DFT calculation at the M06-2X/6-31G­(d) level of theory considering the reactant complex with dispersion corrections. The calculated activation energies for empty C₆₀ and Li⁺@C₆₀ (65.2 and 43.6 kJ mol^–1, respectively) agreed fairly well with the experimentally obtained values (67.4 and 44.0 kJ mol^–1, respectively). According to the calculation, the lowering of the transition state energy by Li⁺ encapsulation was associated with stabilization of the reactant complex (by 14.1 kJ mol^–1) and the [4 + 2] product (by 5.9 kJ mol^–1) through favorable frontier molecular orbital interactions. The encapsulated Li⁺ ion catalyzed the Diels–Alder reaction by lowering the LUMO of Li⁺@C₆₀. This is the first detailed report on the kinetics of a Diels–Alder reaction catalyzed by an encapsulated Lewis acid catalyst rather than one coordinated to a heteroatom in the dienophile