Molecular electronics describes a field that seeks to implement electronic components made of molecular building blocks. To date, few studies have used conjugated polymers in molecular junctions despite the fact that they potentially transport charge more efficiently than the extensively investigated small-molecular systems. Here we report a novel type of molecular tunnelling junction exploring the use of conjugated polymers, which are self-assembled into ultrathin films in a distinguishable ‘planar’ manner from the traditional vertically oriented small-molecule monolayers. Electrical measurements on the junctions reveal molecular-specific characteristics of the polymeric molecules in comparison with less conjugated small molecules. More significantly, we decorate redox-active functionality into polymeric backbones, demonstrating a key role of redox centre in the modulation of charge transport behaviour via energy level engineering and external stimuli, and implying the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.