Main chain liquid crystalline polytriazoles with aggregation-induced emission characteristics: click polymerization, mesomorphic packing, and solid state emission

Biphenyl-containing diazides and diynes carrying tetraphenylethylene units are designed and synthesized. Their "click" polymerizations are initiated by Cu(PPh3)3Br in THF or DMF, affording soluble, regioregular polytriazoles in high yields (up to 94.8%) with narrow molecular weight distributions. The structures and properties of the polymers are evaluated and characterized by IR, NMR, UV, PL, TGA, DSC, POM and XRD measurements. All the polymers are almost nonluminescent when dissolved in solutions but become highly emissive when aggregated in poor solvents or fabricated as thin films in the solid state, displaying a novel phenomenon of aggregation-induced emission. The photophysical properties of the polymers are sensitive to their molecular structures and their solid-state quantum yields decrease with an increase in the spacer length. All the polymers enjoy high thermal stability, with 5% weight loss occurring at temperatures up to 406 °C. They are mesomorphic. While polymers with rigid main chains exhibit nematicity, those with longer spacer lengths show better mesogenic packing and hence form sematic phases at higher temperatures.