Influence of the π‐bridge and heteroatom on fluorene‐based donor‐acceptor polymers: Structure and optoelectronic properties

Abstract Conjugated copolymers possess intriguing electronic characteristics that can be precisely modulated by manipulating their chemical structures. In this study, we explored two approaches for fine‐tuning the energy levels of these copolymers: the incorporation of heterocyclic moieties between the donor and acceptor units, and the substitution of a chalcogen atom in the acceptor unit. Specifically, we investigated the insertion of a thiophene along the polymer backbone and the replacement of sulfur with selenium in the acceptor unit. A series of copolymers were synthesized and thoroughly characterized using both experimental and theoretical methods. Partial density distribution of states analysis revealed that the inclusion of a thiophene significantly altered the HOMO level. Furthermore, the resulting Eg exhibited a decrease of approximately 0.8–0.9 eV compared to the copolymer without thiophene, indicating an enhanced planarization of the chain and increased conjugation length. Experimental data obtained from cyclic voltammetry demonstrated that both the conjugation length and the chalcogen atom in the acceptor unit played crucial roles in controlling the energy levels of the HOMO and LUMO. These findings establish a clear correlation between the chemical structure and the properties of the copolymers, demonstrating the potential for precise control and tailoring of their electronic characteristics.