Poly(2,6-azuleneethynylene)s: design, synthesis, and property studies

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-to-head, and tail-to-tail segments, of which the head-to-tail one accounts for about 27% (determined from 1H 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(p-phenyleneethynylene)s (PPEs), PAzE-1 and PAzE-2 are ambipolar semiconductors.