First principle studies of charge transport in PPV polymer under conformational deformation

We consider the inclusion of torsional deformations in the structure of an infinite chain of poly-p-phenylene vinylene and study the consequences on charge transport along the polymer length. Calculations of the electronic transport are performed with density functional theory combined with Keldysh nonequilibrium Green's function method. Deformations are modeled either as a sharp rotation of the polymer backbone about a single chemical bond or as a continuous twist extending along various monomer units. We study current-voltage (I-V) characteristics in a two probe configuration as a function of angle and degree of torsional sharpness and demonstrate that when the backbone torsion is abrupt a barrier to electron transport builds up that becomes maximum at an angle of 100°. The outcome of our calculations is that the abrupt twist of the polymer backbone creates two virtually disconnected segments, which validates models that treat a real polymer as distribution of chains of different sizes and conjugation lengths.