Invited Speaker: Iain McCulloch

Start date:August 8, 2018 at 08:30

Low Conformational Disorder Semiconducting Polymers for Organic Electronic Applications

Synthesis of conjugated aromatic polymers typically involves carbon coupling polymerisations utilising transition metal catalysts and metal containing monomers. This polymerisation chemistry creates polymers where the aromatic repeat units are linked by single carbon-carbon bonds along the backbone. In order to reduce potential conformational, and subsequently energetic, disorder due to rotation around these single bonds, an aldol condensation reaction was explored, in which a bisisatin monomer reacts with a bisoxindole monomer to create an isoindigo repeat unit that is fully fused along the polymer backbone. This aldol polymerization requires neither metal containing monomers or transition-metal catalysts, opening up new synthetic possibilities for conjugated aromatic polymer design, particularly where both monomers are electron deficient. The condensation reaction locks the repeat units together with a carbon-carbon double bond link, eliminating free rotation of the repeat units and thus rigidifying the polymer conformation. Polymers with very large electron affinities can be synthesised by this method, resulting in air stable electron transport, demonstrated in solution processed organic thin film transistors. The rigid, planar nature of the backbone also facilitates extended delocalisation of both frontier molecular orbitals and a subsequently low bandgap. We present an electrical, optical and morphology characterisation of polymer thin films, illustrating structure-property relationships for this new class of polymers.