Revealing the Intricate Optical Spectra of Organic Open-Shell Conjugated Polymers

Organic semiconductors based on conjugated donor-acceptor (D-A) polymers are a unique platform for electronics devices, spintronics, and energy harvesting opportunities. Developing a better understanding of the electronic structure of D-A polymers, especially with high-spin states, is necessary to create next-generation technologies. Herein, we investigate the optoelectronic properties of open-shell D-A polymers using density functional theory (DFT) and advanced computational methods such as GW approximation and Bethe-Salpeter equation (BSE). Using the spin-polarized method, including spin-orbit coupling (SOC), we demonstrate the open/close-shell, strong electron correlation, narrow bandgap, and dielectric properties. The electron occupancy in the valence band (VB) and conduction band (CB) and repositioning of electrons from the VB to CB along different wave vectors reveals localized spins in the polymer backbone articulating multiradical character. The optical spectra computed using the BSE approach accurately predict the exciton peak and agree with the polymers' experimental optical gap.