[2,2′]paracyclophane-based π-conjugated molecular wires reveal molecular-junction behavior

The electronic coupling as well as the attenuation factor (β), which depends primarily on the nature of the molecular bridge and is used as a benchmark to test the molecular wire behavior, have been determined in a systematic study carried out on a series of ZnP/C60 conjugates connected through a [2,2′]paracyclophane−oligophenylenevinylene (pCp-oPPV). The convergent synthesis involves a series of Horner−Emmons olefination reactions or double palladium-catalized Heck-type reactions. ZnP−pCp−C60 conjugates were finally obtained by the 1,3-dipolar cycloaddition reaction of the in situ-generated azomethyne ylide containing the ZnP−pCp moiety to the [60]fullerene using Prato conditions. Experimental (UV−vis, fluorescence, transient absorption spectroscopy, and solution electrochemistry) and theoretical studies revealed that the pCps act as molecular junctions. If hole transfer is assumed to be the dominant charge transfer (CT) mechanism, CT is facilitated in one direction (from C60 to ZnP via pCp) but disfavored in the other direction (from ZnP to C60 via pCp).