Tuning Charge Transport Properties of Asymmetric Molecular Junctions

Charge transport characteristics of asymmetric :molecules containing a 9,9 '-spirobitluorene platform coupled covalently to a phenylene ethynylene linker capped with either a thiol or a nitrile end group are investigated by break junction techniques. It is shown that the platform provides very good electronic coupling with metallic leads and the differences in the charge transport depend solely on the type of the anchoring group at the opposite end of the molecule. The SH-terminated molecule has 1 order of magnitude higher conductance compared to the CN-terminated one, and the charge transport path depends on the end,group utilized. By a combined :experimental break junction techniques and theoretical DFT calculations, it was demonstrated that in molecules containing SH- terminated phenylene ethynylene Wire attached to the 9,9 '-spirobifluorerie platform the charge is transported through fluorene unit and covalently coupled :phenylene ethynylene linker.' For CN-terminated molecules charge is transported through the thiolate termini olthe 9,9 '-spirobifluorene tripod. These :studies demonstrate the potential of spinbifluorene platform for the bottom-up approach to Molecular architectures by its immobilization with all three thiol groups to one of the electrodes without compromising,charge transport via the conjugated backbone.