Electrochemical Benzylation of [60]Fullerene-Fused Lactones: Unexpected Formation of Ring-Opened Adducts and Their Photovoltaic Performance

Abstract

Electrochemical benzylation of [60]­fullerene-fused lactones with different motifs unexpectedly affords three types of ring-opened benzylated adducts under different conditions. Both [60]­fullerene-fused δ- and γ-lactones can be benzylated to generate ring-opened mono- and bis-benzylated adducts in good yields. In addition, representative fullerene products have been applied as efficient electron-transport materials in perovskite solar cells.

Retro Baeyer–Villiger reaction: thermal conversion of the [60]fullerene-fused lactones to ketones

“…of PhCH 2 Br at 50 °C for 6 h, we obtained two ring-opened bis-benzylated peroxyesters 3a (29% yield) and 4a (25% yield), rather than the expected keto analogues. 6,18 The oxygen atoms in the products should come from a trace of O 2 in the system, 19 and the selectivity for 3a and 4a was comparable to that for 6 and 7 (Fig. 1) obtained from the C 60 -fused lactone reported earlier by us.…”

“…Subsequently, we investigated the reaction of the C 60 -fused lactone dianions with benzyl bromide (PhCH 2 Br), and ring-opened benzyl adducts were unexpectedly obtained. 6 In addition, the ring-opened products could be used as the efficient electron-transport materials (ETMs) in perovskite solar cells (PSCs), and a slightly higher power conversion efficiency (PCE) than that of [6,6]-phenyl-C 61butyric acid methyl ester (PCBM) was obtained.…”

“…1) obtained from the C 60 -fused lactone reported earlier by us. 6 Due to the similarity of the peroxyester groups in 3a and 4a to the ester groups in 6 and 7, we compared their 13 C NMR spectra and found that they were nearly the same except for the chemical shifts for the carbonyl group and a few aryl carbons (see the ESI † Fig. S25 and S26).…”

“…Characteristic potential values and the energy levels of 3a-5a along with 2a, 6-8 and PCBM derived from DPV a Versus ferrocene/ferrocenium. Experimental conditions: 1.0 mM of compound and 0.1 M of tetra-n-butylammonium perchlorate (TBAP) in anhydrous 1,2-C 6 H 4 Cl 2 ; reference electrode: SCE; working electrode: Pt disc; auxiliary electrode: Pt wire; step potential: 4 mV; pulse amplitude: 50 mV; pulse duration: 0.2 s; pulse period: 0.5 s. b Estimated using the following equation: LUMO level = À(4.8 + E 1 ) eV.20c Half-wave potentials and the LUMO levels of 2a, 6-8 and PCBM are cited from our previous studies 5,6. …”

Successively Regioselective Electrosynthesis and Electron Transport Property of Stable Multiply Functionalized [60]Fullerene Derivatives

“…Even though we could capture the intermediate leading to the cyclized 1,2,4,17-adduct, the instability of this unique cyclized product precluded its characterization by 13 C NMR and single-crystal X-ray analysis. Bearing the aforementioned different reactivity of the same dianionic species toward alkylating and acylating reagents and instability of the previously obtained tetrafunctionalized product in mind, our continuous efforts in electrochemical functionalization of fullerene derivatives [25,28,29,[38][39][40][41] stimulated us to investigate the reaction of the dianionic [60]fulleroindolines 1a-c 2-with phthaloyl chloride in order to contrast their reactivity behavior and to see if the unprecedented tetrafunctionalized cis-3 ′ isomers (type G) and "S"-shaped hexafunctionalized products (type H) bearing two acyl groups can be generated in the present case [42]. It turns out that these two unique types of tetra-and hexafunctionalized products can be successfully synthesized and are stable up to 107−275°C.…”