Synthesis and characterization of new luminescent 1,10-phenanthroline- and pyridine-containing π-conjugated polymers. Their optical response to protic acid, Mⁿ⁺, and solvents

New π-conjugated polymers comprised of alternating 1,10-phenanthroline/1,4-didodecyl-oxybenzene, 1,10-phenanthroline/9.9-dioctylfluorene, or pyridine/1,4-dialkoxybenzene units were prepared by palladium(0)-catalyzed coupling reaction in 84-98% yields. The derived polymers gave M_n of 5400-8800 in GPC analysis, and they possessed good solubility in organic solvents and high thermal stability. Electrochemical reduction (or n-doping) of the polymers proceeded with peaks in the range -2.3 to -2.6 V vs Ag⁺/Ag. The polymers were highly photoluminescent, and strong blue emission with the peak in the range 412-434 nm was observed in solutions. The emission peak as well as the UV-vis absorption peak of the polymer was influenced by the solvent polarity, protonation, and formation of metal complexes. When the polymers were protonated with trifluoroacetic acid, a large red-shift (ca. 40-60 nm) of the absorption peak was observed. The photoluminescent properties of the polymers were tuned by coordination of the polymer with metal ions. Polymers with long side chains formed an ordered structure in the solid state as judged from their XRD patterns.