Optical and electronic properties of crystalline poly(para-phenylene) by first-principles calculations and experimental results

We have performed first-principles LDA band structure calculations for 1D and 3D crystalline poly(para-phenylene) using the LAPW and the pseudopotential method, which are based on the density functional theory. The band gap can be easily tuned through the whole visible region by varying the structural parameters. Optimized structural parameters have been determined for the orthorhombic space group Pbam and the 1D chain. We predict a torsion angle between two adjacent rings of 18° for the 3D structure and 27° for the 1D chain. The interchain coupling leads to band splittings of nearly 1 eV. The absorption coefficient has been calculated and compared to experimental data. The excellent agreement indicates that excitonic effects are weak. Calculations of the luminescene emission efficiency are presented.