Effect of Stacking Interactions on the Spectra of the Monomer of PFBT: A Theoretical Study
Jing Wang, Jiande Gu and Jerzy Leszczynski

Conjugated polymers (CPs) contain one π-conjugated backbone and functional groups that could be ionized
in high dielectric media. These materials combine the semiconducting and photon harvesting properties of
electronically delocalized polymers with the charge-mediated behavior of polyelectrolytes. CPs can be used
as highly responsive optical sensors for chemical and biological targets. The density functional theory (DFT)
and the time-dependent density functional theory (TDDFT) approach were employed to simulate the absorption
and emission spectra of poly[9,9′-bis(6′′-N,N,N-trimethylammonium)hexyl]fluorene-co-alt-4,7-(2,1,3-benzothiadiazole)
dibromide] (PFBT) in the present study. The influences on the spectra of the monomer unit
F(BT)F due to stacking with the fluorene (F) and 2,1,3-benzothiadiazole (BT) units have been explored. The
results suggest that stacking lowers the excitation and emission energy, facilitating detections of the polymers.