Fulleropyrrolidine End-Capped Molecular Wires for Molecular ElectronicsSynthesis, Spectroscopic, Electrochemical, and Theoretical Characterization

In continuation of previous studies showing promising metal−molecule contact properties a variety of C60 end-capped “molecular wires” for molecular electronics were prepared by variants of the Prato 1,3-dipolar cycloaddition reaction. Either benzene or fluorene was chosen as the central wire, and synthetic protocols for derivatives terminated with one or two fullero[c]pyrrolidine “electrode anchoring” groups were developed. An aryl-substituted aziridine could in some cases be employed directly as the azomethine ylide precursor for the Prato reaction without the need of having an electron-withdrawing ester group present. The effect of extending the π-system of the central wire from 1,4-phenylenediamine to 2,7-fluorenediamine was investigated by absorption, fluorescence, and electrochemical methods. The central wire and the C60 end-groups were found not to electronically communicate in the ground state. However, the fluorescence of C60 was quenched by charge transfer from the wire to C60. Quantum chemical calculations predict and explain the collapse of coherent electronic transmission through one of the fulleropyrrolidine-terminated molecular wires.