Theoretically designated synthesizable donor-acceptor type semiconducting copolymers: Investigation into molecular, electronic, and optical properties

Abstract

Semiconducting organic polymers with donor-acceptor units are of great interest due to their superior properties. Tuning the HOMO and LUMO levels with different donors and acceptors makes it possible to design polymers with desired electronic, optical, and molecular properties. In this paper, commercially available donors (thieno[3,4-b]pyrazine (TP), thieno[3,4-b]quinoxaline (TQ), 2H-pyrrolo[3,4-b]quinoxaline (PQ), 6H-pyrrolo[3,4-b]pyrazine (PP)) and acceptors (benzo[c][1,2,5]thiadiazole (BT), naphtho[2,3-c][1,2,5]thiadiazole (NT)) were selected to form monomers (TP-BT, TP-NT, TQ-BT, TQ-NT, PP-BT, PP-NT, PQ-BT, PQ-NT) that were used to design D-A type copolymers. The electronic and optical properties of the monomers and oligomers were theoretically investigated using DFT/B3LYP/6-31G** and TD-DFT/B3LYP/6-31G** methods. The HOMO and LUMO levels of the designed polymers ranged from −5.05 to −4.18 eV and from −3.05 to −3.57 eV, respectively. Estimated electronic band gaps of these polymers were obtained as 0.79–2.00 eV within the range of semiconductor values. It is indicated that TQ/PQ units as donors and BT as an acceptor is the suggestible combination to design low band gap polymer which is easily synthesizable through direct arylation polymerization of brominated acceptors with donors. The presented approach provides a valuable guide for experimental studies to design new types of semiconducting organic polymers.