DFT study of electronic band structure of alternating triphenylamine-fluorene copolymers

Triphenylamine-fluorene alternating copolymers TPAFn (n = 1–3) can be employed as hole transport layer and blue light-emitting materials of the (multilayer) polymeric light-emitting diodes. In this work we investigate their electronic band structures using the solid state density functional theory (DFT) approach. All polymers are treated as one-dimensional infinite conjugated chains generated by applying periodic boundary condition to their repeat units. We consider six DFT approximations (PBE1PBE, B3LYP, O3LYP, OB95, PBEPBE, and TPSSTPSS) in this study. 6-31G(d) basis set and 32 k points are employed in all calculations. We compare the electronic band gaps (Egapʹs), and highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energy levels with experimental data. In all DFT calculations for TPAFnʹs, the best agreement with experiment is obtained with hybrid DFT functionals for band gaps and ionization potentials (IPʹs). For electron affinities (EAʹs), the gradient-corrected functionals perform better. Based on the computational results, TPAF1 would be predicted to be the best material for the electron-blocking/hole transport layer.