Tuning the HOMO-LUMO energy gap in conjugated polymers via doping: a pathway towards flexible electronics

The growing demand for miniaturized and flexible electronics highlights the inherent structural and mechanical limitations of traditional inorganic materials. Conjugated organic polymers (COPs) have emerged as a promising class of materials for next-generation electronic devices, yet enhancing their electrical conductivity remains a critical objective. Herein, we report a theoretical investigation of the structural, energetic, electronic, and spectroscopic properties of pristine and doped polythiophene (PTh) and polypyrrole (PPy) oligomers. The doping process was modeled via electron removal and charge compensation by a ClO₄^- anion. Doping induces the formation of polaronic and bipolaronic states, which is accompanied by a substantial reduction in the HOMO-LUMO gap (E_gap). These results indicate a marked enhancement in the electrical conductivity of the polymers.

DFT and TD-DFT calculations were conducted using the PBE0 functional along with Pople's split valence 6-31G(d,p) basis set, which includes polarization functions on all atoms.