Statistical copolymers of thiophene-3-carboxylates and selenophene-3-carboxylates; 77Se NMR as a tool to examine copolymer sequence in selenophene-based conjugated polymers

Abstract

Herein, we demonstrate that homopolymerization and statistical copolymerization of 2-ethylhexyl thiophene-3-carboxylate and 2-ethylhexyl selenophene-3-carboxylate monomers is possible via Suzuki–Miyaura cross-coupling. A commercially available palladium catalyst ([1,3-bis(2,6-di-3-pentylphenyl)imidazol-2-ylidene](3-chloropyridyl)dichloropalladium(II) or PEPPSI-IPent) was employed to prepare regioregular conjugated polymers with high molecular weights (∼20–30 kg mol⁻¹), and relatively narrow molecular weight distributions. The optical bandgap in the copolymer series could be reduced by increasing the concentration of selenophene-3-carboxylate in the material. Configurational triads were observed in the ¹H NMR spectra of the statistical copolymers, which were assigned using a combination of 2D NMR techniques. The use of a ¹H–⁷⁷Se HSQC spectrum to further examine sequence distribution in the statistical copolymers revealed how ⁷⁷Se NMR can be used as a tool to examine the microstructure of Se-containing conjugated polymers.