  Motivated by an experiment in which the singlet-triplet gap in triphenylene
based copolymers was effectively tuned, we used time dependent density
functional theory (TDDFT) to reproduce the main results. By means of
conventional and long-range corrected exchange correlation functionals, the
luminescence energies and the exciton localization were calculated for a
triphenylene homopolymer and several different copolymers. The phosphorescence
energy of the pure triphenylene chain is predicted accurately by means of the
optimally tuned long-range corrected LC-PBE functional and slightly less
accurate by the global hybrid B3LYP. However, the experimentally observed fixed
phosphorescence energy could not be reproduced because the localization pattern
is different to the expectations: Instead of localizing on the triphenylene
moiety - which is present in all types of polymers - the triplet state
localizes on the different bridging units in the TDDFT calculations. This leads
to different triplet emission energies for each type of polymer. Yet, there are
clear indications that long-range corrected TDDFT has the potential to predict
the triplet emission energies as well as the localization behavior more
accurate than conventional local or semi-local functionals.
