Synthesis of polyphenylenes through bergman cyclization of enediynes with long chain alkyl groups

Several new enediynes with long chain alkyl groups were synthesized through Sonogashira coupling reactions between long chain alkynes and (Z)-1,2-dichloroethene. These enediynes (1) were then subjected to thermal Bergman cyclization in a refluxing diphenyl ether bath under vacuum to obtain conjugated polyphenylenes with the weight-average molecular weights up to 4.9 × 10³ g·mol⁻¹. The occurrence of Bergman cyclization was confirmed by ¹H-NMR, ¹³C-NMR, and IR spectroscopic analysis. These polyphenylenes are fully soluble in common organic solvents and exhibit good thermal stability. The optical properties of the polyphenylenes were investigated by UV-Vis absorption and photoluminescence (PL) spectroscopies. A blue emission was observed for all these polyphenylenes.