Torsional effects on the optical properties of PPV and PPP

International audience; The optical properties of infinite and isolated chains of poly(para-phenylene vinylene) (PPV) and poly(para-phenylene) (PPP) are studied using Density Functional Theory (DFT) in the Local Density Approximation (LDA) with norm-conserving pseudopotentials to replace the core electrons. We investigate theoretically the influence of several structural modifications of conjugated polymers on the band gap and the optical properties. Our results show that the band gap for isolated chains of PPV depends on the chain length. We also find that for both PPV and PPP one-dimensional chain polymers, the optical properties are strongly affected by the torsion angles.