Highly Fluorescent Conjugated Copolymers Constructed by Alternating Heterocyclic Diazoles and Alkoxy Benzene

Abstract

Highly fluorescent copolymers Oxa‐Bz and Thia‐Bz consisting of alternating heterocyclic diazole derivative and alkoxy benzene were designed and regioselectively synthesized by the Suzuki–Miyaura reaction with a palladium catalyst. Density functional theory calculation of modeling the repetitive unit suggested the possibility of full conjugation along the polymer chain and the occurrence of intramolecular electron transfer in which the alkoxy benzene moiety was the electron donor and the diazole moiety was the electron acceptor. The extension of conjugation length from the corresponding monomers to the copolymer was confirmed by electrochemical analysis. The redox potentials of the resulting copolymers were significantly reduced in comparison with those of the monomers. The photophysical properties, including absorption and emission spectra, also showed that the energies of the frontier orbitals changed after the covalent bonding between the electron donor and acceptor groups. Moreover, the emission of these two copolymers showed solvent‐dependence, whereby the emission band shifted to longer wavelengths in higher polarity solvents. The fluorescence quantum yields of Oxa‐Bz reached 68% and that of Thia‐Bz 71%. This strong fluorescence might be guaranteed by the rigidity of these copolymers.