ABSTRACT: Stacked models that include 9,90-bis(600-N,N,N-trimethylammonium)
hexyl]fluorene-co-alt-4,7-(2,1,3-benzothiadiazole)dibromide
(F(BT)F) monomer sandwiched between two stacked 2,1,3-benzothiadiazole
(BT) units were explored using theoretical approaches. Molecular
structures and the optical characteristics of the investigated species were
investigated at the M06-2X/6-311G(d,p)//TD-M06-2X/6-311G(d,p)
level of theory. In all models, the electronic excitation to the lowest singlet
ππ* excited state (S1(ππ*)) is governed by the highest occupied
molecular orbital to lowest unoccupied molecular orbital (HOMO f
LUMO) transitions. The obtained results suggest that stacking interaction might have only minor effects on the transition energy for
both absorption and emission processes. Instead, the reduction in the excitation energy of the stacked complexes should be
attributed to the dipoledipole interaction. The larger the interaction energy of the stacked models, the bigger the observed
differences between absorptionemission energies. The presence of the solvation medium with small dielectric constant may
increase the absorptionemission energy differences. It is expected that the largest absorptionemission shift can be observed in
the benzene solution.