Modulating the Properties of Azulene-containing Polymers Through Functionalization at the 2-Position of Azulene

Poly(2-arylazulene-alt-fluorene) and poly(2-arylazulene-alt-thiophene) are synthesized via Suzuki and Stille cross-coupling polymerization, respectively, using 1,3-dibromo-2-arylazulenes as monomers, which are prepared by a novel directed C-H activation method of 2-carboxylic azulene and subsequent bromination reaction. Our study shows that functionalization at the 2-position of azulene monomers influences polymer properties. For instance, different from electron-withdrawing groups that discourage the protonation of azulene, electron-donating aryl groups, however, enhances the sensitivity of response to acid. Protonation of the polymers leads to significant shifts in absorption spectra accompanying with obvious color changes from green to brown in majority cases because of the formation of poly(azulenium cation). The electrochromic properties of polymers are examined, exhibiting that nature of aryl group at the 2-position of azulene influences the stability of their electrochromic devices.