Fulleropyrrolidine molecular dumbbells act as multi-electron-acceptor triads. Spectroscopic, electrochemical, computational and morphological characterizations

Abstract

We synthesized three dumbbell-like compounds 2a-c, each containing two C60 groups at the periphery and pyromellitic diimide (PMDI) in the middle, and examined their electronic as well as assembly characteristics with both experimental and computational methods. Cyclic voltammetry (CV) measurements revealed that each of three electron-accepting (AAA) triads could accommodate up to eight electrons. Computational studies (density functional theory, DFT) of 2a-c at PBEPBE/6-311G(d,p) level of theory, with B3LYP/6-31G(d) optimized geometries, revealed that HOMO-LUMO energy gaps are similar to those of the model compound [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Compounds 2a-c were also found to assemble into vesicles and nanoparticles on the copper grid (100-300 nm, TEM), while giving more sizeable aggregates after a deposition on the glass (SEM, >5 μm). Understanding the packing of 2a-c on various solid substrates, as well as the assembly characteristics in general, is important for tuning the properties and fabrication of electronic/optical devices. On the basis of the results of conformational analysis (MM and DFT calculations), we deduced that different alkyl spacers in 2a-c ought to play a role in π-π interactions between the aromatic components of the triad to guide the packing and therefore morphology of the material.