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Abstract A new class of conjugated macrocycle, the cyclo[4]thiophene[4]furan hexyl ester (C4TE4FE), is reported. This cycle consists of alternating α‐linked thiophene‐3‐ester and furan‐3‐ester repeat units, and was prepared in a single step using Suzuki–Miyaura cross‐coupling of a 2‐(thiophen‐2‐yl)furan monomer. The ester side groups help promote asynconformation of the heterocycles, which enables formation of the macrocycle. Cyclic voltammetry studies revealed that C4TE4FE could undergo multiple oxidations, so treatment with SbCl₅resulted in formation of the [C4TE4FE]²⁺dication. Computational work, paired with¹H NMR spectroscopy of the dication, revealed that the cycle becomes globally aromatic upon 2e⁻oxidation, as the annulene pathway along the outer ring becomes Hückel aromatic. The change in ring current for the cycle upon oxidation was clear from¹H NMR spectroscopy, as the protons of the thiophene and furan rings shifted downfield by nearly 6 ppm. This work highlights the potential of sequence control in furan‐based macrocycles to tune electronic properties. 

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 1 H NMR spectra of the statistical copolymers, which were assigned using a combination of 2D NMR techniques. The use of a 1 H– 77 Se HSQC spectrum to further examine sequence distribution in the statistical copolymers revealed how 77 Se NMR can be used as a tool to examine the microstructure of Se-containing conjugated polymers.