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

Abstract

A class of nonbenzenoid analogues of poly(pphenylenevinylene)s (PPVs), 2,6-azulene-vinyl-based conjugated polymers (CPs) r-PAzV, hhtt-PAzV, and ht-PAzV, have been reported with different dipole arrangements of azulene units, where the five-membered ring and seven-membered ring of azulene core are defined as "head (H)" and "tail (T)", respectively. The PAzV polymers exhibit diverse backbone structures, proton responsiveness, an unusual relationship between crystallinity and regioregularity relative to conventional CPs, and balanced ambipolar charge transport. In regiorandom r-PAzV, the proportions of the H−T, H−H, and T−T linkages are about 40, 20, and 40%, respectively. The studies on solubility, thermal/optical properties, and microstructures of these PAzV polymers reveal that the presence of H−H and T−T arranged moieties in r-PAzV and hhtt-PAzV strengthens interchain interactions. Grazing-incidence wide-angle X-ray scattering measurements demonstrate enhanced long-range order with up to four orders of side-chain stacking reflections in as-spun films of r-PAzV and hhtt-PAzV. Williamson−Hall and Scherrer's analyses indicate that the lamellar crystallites in films of ht-PAzV have a much smaller size and lower crystallite quality relative to r-PAzV and hhtt-PAzV. Therefore, organic thin-film transistors based on r-PAzV and hhtt-PAzV display 2−4 orders higher charge carrier mobilities than those of ht-PAzV-based devices. The poor device performance of ht-PAzV might be attributed to the gradient electrostatic potential distribution and localized distribution of the Frontier molecular orbitals of the main chain. Our work enriches the family of PPV-like polymers, achieves the regulation of dipole arrangements of 2,6-azulene units together with clear structural analysis, and discloses that the dipole arrangements of azulene units along the polymer backbone have a great influence on the assembly of polymer chains.