Synthesis of soluble meta-linked phenylene-based polymer and the peculiarities in photoluminescence properties

A soluble meta-linked phenylene-based polymer P1 was synthesized by Yamamoto coupling of a 5,5′-dibromo-2,2′-dibutoxy-biphenyl monomer and was characterized by microanalysis, FT-IR, 1H NMR and GPC. The molecular weight of P1 is more than 6000 g/mol. The P1 has good solubility in most organic solvents and good film-formation property. P1 shows the main absorption band at 248 nm with a weak shoulder at 280 nm in solution and the fluorescence emission centered at 374 nm whose intensities strongly depend on the excitation energy localized on both absorption bands. An increase in absorption intensity of 280 nm band and less dependence between fluorescence intensity and excitation energy are found as P1 in film state. The spectral peculiarities are thought to be related to the presence of two stable conformations with twisted angles of 144° and 180° along rotation-permitted axes in polymer chain. The result of theoretical calculations for the absorption spectrum of the model compound is accordant with the proposed conformers in polymer chain.