Polynorbornenes with pendant perylene diimides for organic electronic applications

Perylene-3,4,9,10-tetracarboxylic diimides (PDI) have been linked to norbornene through either an imide or a bay'' position. These PDI-functionalised norbornenes are readily polymerised using a ruthenium ring-opening metathesis polymerisation (ROMP) initiator. In one case the polymerisation is shown to be well controlled with a linear dependence of molecular weight on the monomer/initiator ratio. For the polymers with PDI-norbornene linkages through the imide nitrogen, UV-vis spectroscopy suggests significant PDI aggregation both in dilute solution and the solid state, a powder X-ray diffraction peak attributable to pi-stacking is seen, and weak n-channel field-effect transistor behavior (electron mobilities <5 x 10(-5) cm(2) V-1 s(-1)) was observed. In contrast, the bay''-linked polymer shows essentially monomer-like UV-vis spectra in both solution and the solid state, no X-ray evidence for pi-stacking, and no measurable transistor behaviour. The polymers were used as acceptors in bulk heterojunction solar cells in combination with poly(3-hexylthiophene): low power conversion efficiencies (<= 0.38%) were obtained, largely due to low short-circuit currents, again with the bay''-linked polymer giving the poorest performance.