The Impact of Copolymer Molecular Sequence on Electronic Transport

Established relationships describe how the energetics and spacing of polarons impact electronic transport in conjugated homo-polymers, yet no model exists extending these concepts to the growing field of sequence-controlled co-polymers. This work employs oxidative molecular layer deposition (oMLD) to form thin films of sequence-controlled copolymers of 3,4-ethylenedioxythiophene (EDOT) and pyrrole (Py) and identifies that molecular sequence drives a three-orders-of-magnitude change in conductivity at fixed composition. We extend Boltzmann hopping transport models for homopolymers to describe how electron energy well depth changes with EDOT and Py copolymer block lengths and separation distances. We measure a critical hopping distance of four monomer units (corresponding to ∼1.5 nm) and a critical polaron formation size of similar length. The model and conceptual insights we develop describe the electronic properties of sequence-controlled copolymers and provide an upper length-scale bound for molecular design of engineered organic nanomaterials.