Synthesis of hyperbranched conjugated polymers based on 3-hexylthiophene, triphenylamine and benzo [c] [1,2,5] thiadiazole moieties: convenient synthesis through suzuki polymerization and impact of structures on optical properties

Novel 3-hexylthiophene-based hyperbranched conjugated polymers containing triphenylamine and benzo [c] [1, 2, 5] thiadiazole moieties were synthesized by Suzuki coupling polymerization of tris (4-bromophenyl) amine, 2,2'-(3-hexylthiophene-2,5-diyl) bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) and 4,7-dibromobenzo [c] [1, 2, 5] thiadiazole. Organic solvent-soluble polymers with number-average molecular weights of 24,000 and 42,000 g/mol were obtained in 54-57 % yields. Their structures, molecular weights and thermal properties were characterized via proton nuclear magnetic resonance (H-1 NMR) and Fourier transform infrared (FT-IR) spectroscopies, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and wide-angle powder X-ray diffraction (XRD) measurements. Optical investigation by UV-vis and fluorescence spectroscopies revealed that the incorporation of the benzo [c] [1, 2, 5] thiadiazole moiety in the hyperbranched polymer structure resulted in a red-shift of the maximum absorption wavelength and an increase in the solution-photoluminescence quantum yield, indicating an extension of the conjugation length. The UV-vis, DSC and XRD results demonstrated that the aggregation of conjugated polymer chains could effectively be reduced by the hyperbranched structures and that conjugation length extension via the introduction of benzo [c] [1, 2, 5] thiadiazole units led to the coexistence of both crystalline and amorphous phases in the solid state and in solution upon addition of a non-solvent.