ИСТИНА

Efficient synthetic route to tightly bound double-caged [60]fullerene derivatives has been developed through lithium salt-assisted [2+3]-cycloaddition. The bispheric molecules feature rigid linking of the fullerene spheres via a four-membered cycle and a pyrrolizidine bridge with an ester function CO2R, which can be varied due to easy accessible starting glycine ester. Here we report a series of such double-caged fullerene derivatives with alkyl substituent (hereinafter, d[60]FR), which have been prepared and characterized by UV/Vis- and NMR spectroscopy, X-ray diffraction, cyclic voltammetry. Variation of the ester alkyl chain significantly improves solubility without affecting the electronic properties. Cyclic voltammetry studies revealed three closely overlapping pairs of reversible peaks due to consecutive one-electron reductions. Rigid pyrrolizidine and cyclobutane moieties provide tight linkage of the two fullerene cages thus enhancing intramolecular electronic communication and ensuring small reorganization energy. X-Ray diffraction analysis shows that the coordination number of d[60]FR equals 9, which is higher than in the PCBM single crystal without solvent impurities [1]. An application of double-caged fullerenes in OSC allowed a two-fold increase in power conversion efficiencies of as-cast P3HT/d[60]FR devices compared to the P3HT/PCBM ones. This is attributed to their good solubility and enhanced charge transport properties, both intramolecular, due to tightly linked fullerene cages, and intermolecular, due to large number of close contacts between the neighboring double-caged molecules. Surprisingly low optimal content of double-caged fullerene acceptor in the photoactive layer (ca 30 wt%) favored better light harvesting and carrier transport due to larger content of P3HT and its higher degree of crystallinity. The reported results suggest good potential of the novel doubled-cage fullerene derivatives with customizable alkyl chain as acceptor materials for organic electronic devices. [1] Paternò G., Warren A. J., Spencer J., Evans G., Sakai V. G., Blumberger J., Cacialli F. J. Mater. Chem. C 2013, 1, 5619–5623.