Synthesis and electrochemical, optical, and thermal properties of polycarbosilanes with silylene–vinylene–phenylene–vinylene backbones and triphenylamine or carbazole unit-containing side chains

Polycarbosilanes with silylene–vinylene–phenylene–vinylene backbones and triphenylamine or carbazole unit-containing side chains were conveniently prepared by Pd-catalyzed one-pot reactions of a trihydrosilane (phenylsilane) with aromatic diynes (p- and m-diethynylbenzene) and triphenylamine or carbazole-unit containing acetylenes. Cyclic voltammetry of these polycarbosilanes suggested that dimerization processes of the pendant units took place during the electrochemical oxidation steps. In UV/vis absorption and emission spectra, the p-phenylene or triphenylamine unit-containing polymers showed λmax peaks at longer wavelength regions than the corresponding m-phenylene or carbazole unit-containing polymers. An energy transfer process from the backbone to the side chain was suggested in the polycarbosilane possessing m-phenylene and triphenylamine units. Photoluminescence quantum yields of these polymers ranged from 0.16 to 0.34 with the m-phenylene and triphenylamine units-containing polymer exhibiting the highest value. DSC analyses revealed that the p-phenylene polymers showed higher glass transition points (148–180 °C) than the corresponding m-phenylene polymers (129–158 °C). In TGA, the 5% weight loss temperatures were in the range of 382–444 °C, suggesting considerably high thermal stability of these polycarbosilanes. Ionization potentials were estimated by atmospheric photoelectron spectroscopy at 5.6–5.9 eV with the values of carbazole polymers being higher than those of the triphenylamine polymers.

Graphical abstractPd-catalyzed one-pot reactions of a trihydrosilane with diynes and functional acetylenes efficiently provided silylene–vinylene–phenylene–vinylene polycarbosilanes with pendant triphenylamine or carbazole units. The resulting polymers exhibited unique electrochemical, optical, and thermal properties, depending on the natures of the main chain and pendant units.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Pd-catalyzed one-pot reactions efficiently provided functionalized polycarbosilanes. ► A resulting polymer exhibited unique photoluminescence via energy transfer. ► The polycarbosilanes showed considerably high thermal stability in DSC and TGA.