Singlet - triplet gaps in polymers from range-separated time dependent density functional theory

The target of the master thesis is to reproduce the experimental results of the singlet-triplet gap tuning of triphenylene based polymers. After introducing the theoretical basics of time dependent density functional theory (TDDFT) and different exchange correlation (XC) functionals, the specific methods and challenges are discussed. By means of standard and long-range corrected (LRC) TDDFT methods, the absorption and emission energies and the triplet localization behavior is calculated then for different types of polymers and one monomer. The experimentally observed fixed phosphorescence energy is not reproduced because the localization pattern is different to the expectations: Instead of localizing on the triphenylene unit - which is the backbone unit of all types of polymers - the triplet state localizes in the TDDFT calculations on the different bridging units. This leads to different triplet emission energies for each type of polymer. However, the phosphorescence energy of the pure triphenylene chain is predicted accurately by means of the LRC-PBE XC functional and slightly less accurate by the standard hybrid B3LYP. Yet, the possible reasons for the deviating results for the other polymers indicate that LRC TDDFT has the potential to predict the triplet emission energies as well as the localization behavior more accurate than with standard XC functionals