Poly(2,6-azuleneethynylene)s: Design, Synthesis, and Property Studies

Abstract

Two poly(2,6-azuleneethynylene)s (PAzE-1 and PAzE-2) were designed and synthesized. The 2,6-azulene units are head-to-tail-arranged in PAzE-1, while there are three types of orientations of 2,6-azulene units in PAzE-2: head-to-tail, head-tohead, and tail-to-tail segments, of which the head-to-tail one accounts for about 27% (determined from 1 H NMR spectra). Such a structural distinction endows the two polymers with different absorption spectra in solution and aggregation states as well as different thin-film morphologies, microstructures, and field-effect transistor (FET) performances, suggesting that the dipole orientation of azulene units in a polymer backbone may be a critical issue that deserves careful consideration during the molecular design and synthesis. PAzE-1 with an ordered dipole orientation has stronger aggregation even in a very dilute solution (10 −6 M). PAzE-2 films have a higher in-plane microstructural order and lower surface roughness than PAzE-1 films; hence, the PAzE-2-based transistor devices exhibit 1−2 orders higher hole and electron mobilities. Unlike typical p-type alkyl-substituted poly(pphenyleneethynylene)s (PPEs), PAzE-1 and PAzE-2 are ambipolar semiconductors.

Poly(2,6-azulene vinylene)s: Azulene Orientation Control and Property Studies

“…The integration ratio of the signals of the vinylenes at δ 7.81, 7.74, and 7.46 ppm is about 1:1:2, indicating that the H–T, H–H, and T–T linkages in r -PAzV account for about 40, 20, and 40%, respectively. It should be noted that the regioregularity of these PAzVs is more clearly understood relative to previous PAzEs and other 2,6-azulene-based CPs. ,,,, …”

“…Then, hhtt -PAzV was prepared via Pd 2 (dba) 3 -catalyzed Stille coupling reactions of M2 with ( E )-1,2-bis­(tributylstannyl)­ethene. The synthesis of ht -PAzV is more challenging than that of the regioregular PAzE . Terminal alkynyl groups can undergo regioselective hydroboration to give trans alkenyl boronates .…”

“…Thus, S1 was prepared according to our previous work (Scheme S3). The CuCl-catalyzed hydroboration of S1 with bis­(pinacolato)­diboron afforded monomer M3 with a yield of 62%. Ultimately, homopolymerization of M3 by Pd­(OAc) 2 -catalyzed Suzuki coupling reaction afforded the regioregular ht -PAzV .…”

“…In comparison with 1,3- and 4,7-connections, the incorporation of 2,6-azulene units into the backbone fully exploits the donor–acceptor (D–A) character of azulene and increases the structural diversity of the resultant polymers through control of the dipole orientation of the azulene units. It has been reported that the D–A structure of 2,6-azulene units is conducive to the formation of compact π–π stacking, , and the dipole arrangements of 2,6-azulene units have a great influence on the material properties and performance. ,− For instance, in 2019, our group synthesized two 2,6-azulene-2,7-fluorene-based CPs and demonstrated that the polymer with disordered dipole arrangement exhibited higher electrical conductivity when doped by trifluoromethanesulfonic acid. , Recently, we realized the solution synthesis of two 2,6-connected polyazulenes and demonstrated that a Nafion composite membrane doped by the regioregular polymer showed a significant increase in proton conductivity and hydrogen fuel cell output power compared to the pristine Nafion membrane . In these polymers, the azulene units were irregularly or 2–2′/6–6′ arranged.…”

“…In these polymers, the azulene units were irregularly or 2–2′/6–6′ arranged. We recently realized the preparation of two types of poly­(2,6-azuleneethynylene) (PAzEs), where the dipole orientations of the azulene units are either highly ordered or random . The regioregular PAzE polymer exhibited a lower degree of crystallinity and lower charge carrier mobilities relative to the regiorandom one.…”