Efficient synthesis and redox behavior of a series of 6-alkyl-2-phenylazulenes

Three new members of 6-alkyl-2-phenylazulene (nPA with n being the number of carbon atoms in the 6-alkyl chain) homologous series, 3a (n=4), 3b (n=6), and 3d (n=10), expected to show smectic E (SmE) phase as a mesophase below fusion, has been synthesized by Pd(PPh3)4 catalyzed Suzuki–Miyaura cross-coupling reaction of the corresponding 6-alkyl-2-bromoazulenes. The redox behavior of 3a, 3b, and 3d including that of their 6-octyl and 6-hexadecyl derivatives 3c (n=8) and 3e (n=16), the synthesis was reported previously, was studied in detail by voltammetric and electrochromic analyses. As the results, amphoteric redox properties with a significant color change were revealed by the nPA homologous series 3a–e, which would be attracted to the application for the device fabrication of the molecular materials.