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 C-60 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 pi-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 Co-60 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 C-60. Quantum chemical calculations predict and explain the collapse of coherent electronic transmission through one of the fulleropyrrolidine-terminated molecular wires.