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

摘要

The target of the master thesis is to reproduce the experimental results ofudthe singlet-triplet gap tuning of triphenylene based polymers. Afterudintroducing the theoretical basics of time dependent density functionaludtheory (TDDFT) and different exchange correlation (XC) functionals, theudspecific methods and challenges are discussed. By means of standard andudlong-range corrected (LRC) TDDFT methods, the absorption and emissionudenergies and the triplet localization behavior is calculated then for differentudtypes of polymers and one monomer. The experimentally observed fixedudphosphorescence energy is not reproduced because the localization patternudis different to the expectations: Instead of localizing on the triphenyleneudunit - which is the backbone unit of all types of polymers - the triplet stateudlocalizes in the TDDFT calculations on the different bridging units. Thisudleads to different triplet emission energies for each type of polymer.udHowever, the phosphorescence energy of the pure triphenylene chain isudpredicted accurately by means of the LRC-PBE XC functional and slightlyudless accurate by the standard hybrid B3LYP. Yet, the possible reasons forudthe deviating results for the other polymers indicate that LRC TDDFT hasudthe potential to predict the triplet emission energies as well as theudlocalization behavior more accurate than with standard XC functionals.