Synthesis and Electrochemical Studies of Bingel-Hirsch Derivatives of M3N@I-h-C-80 (M = Sc, Lu)

Bingel-Hirsch derivatives of the trimetallic nitride template endohedral metallofullerenes (TNT-EMEs) Sc3N@I-h-C-80 and Lu3N@I-h-C-80 were prepared by reacting these compounds with 2-bromodiethyl malonate, 2-bromo-1,3-dipyrrolidin-1-ylpropane- 1,3-dionate bromide, and 9-bromo fluorene. The mono-adducts were isolated and their H-1 NMR spectra showed that the addition occurred with high regioselectivity at the [6,6] bonds of the I-h-C-80 fullerene cage. Electrochemical analysis showed that the reductive electrochemistry behavior of these derivatives is irreversible at a scan rate of 100 mV s(-1), which is comparable to the behavior of the pristine fullerene species. The first reduction potential of each derivative is either cathodically or anodically shifted by a different value, depending on the attached addend. Bis-adducts containing EtOOC-C-COOEt and HC-COOEt addends were isolated by HPLC and in the case of Sc3N@I-h-C-80 the first reduction potential exhibits a larger shift towards negative potentials when compared to the mono-adduct. This observation is important for designing acceptor materials for the construction of bulk heterojunction (BHJ) organic solar cells, since the polyfunctionalization not only increases the solubility of the fullerene species but also offers a promising approach for bringing the LUMO energy levels closer for the donor and the acceptor materials.