Selenophene-bearing low-band-gap conjugated polymers: tuning optoelectronic properties via fluorene and carbazole as donor moieties

In this study, two donor-acceptor (D-A)-type conjugated polymers, namely PQSeCz and PQSeFl, were designed and synthesized. Selenophene was incorporated as the pi-bridge and quinoxaline as an acceptor unit, while carbazole and fluorene were used as the donor units. Polymers were synthesized via palladium-catalyzed Suzuki polymerization reaction. All molecules were characterized by H-1 and C-13 NMR spectroscopy. The weight and number average molecular weights of the two polymers were determined by gel permeation chromatography. Electrochemical and spectroelectrochemical characterizations of the polymers were performed to investigate their optoelectronic properties. Oxidation potentials were 1.15 V/0.82 V and 1.11 V/0.82 V for PQSeCz and PQSeFl, respectively, while reduction potentials were - 1.26 V/- 1.14 V and - 1.48 V/- 1.20 V, respectively. In the visible region, maximum absorption wavelengths for the two polymers were 551 nm and 560 nm, respectively. Optical band gaps (Egop) were found from the lowest energy pi-pi* transition onsets as 1.67 eV for PQSeCz and 1.51 eV for PQSeFl, respectively. Both polymers showed good solubility in common solvents.