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Extension of oxygen-embedded polycyclic aromatic hydrocarbons (PAHs), in particular with a defined topology, is synthetical-ly challenging primarily because of limited regio-specific methods and poor solubility of PAHs. We reported herein an efficient way to construct quinoidal pentacenes and nonacenes with regular zigzag O-inserted edges. These O-embedded backbones composed of benzene, pyranyl and cyclohexa-1,4-diene moieties, provided access to a new class of longitudinally conjugated acenes with superior stability. Their structures, confirmed by single-crystal XRD analysis, indicated that they possessed rich hydrogen/halogen-bonding interactions, which likely contribute to the strengthened aggregation. In contrast to many other O-annulated PAHs generally displaying short-absorption wavelengths due to partially interrupted electron communication, the O-embedded quinoidal acene exhibited highly red-shifted absorptions (up to ~699 nm) and narrowed energy gaps (down to ~1.5 eV). As with more O-containing rings and quinoidal subunits in the backbone, the conjugation size was enlarged and the molar absorption coefficients (ε) of the λmax increased further significantly, in particular of a noticeable lower-energy peak at ~790 nm for O-doping nonacenes N1-OH/OMe. By the thin-film based organic field-effect transistor (OFET) measurements, the relative-ly ordered O-doping pentacene P1-OMe possessed a hole transporting efficiency (µh) of 0.00406 cm-2 V-1 s-1 in in-air fabricated devices, while O-pentacene P1-PFB with two perflurobutoxyl substituents witnessed an improved µh up to 0.0152 cm-2 V-1 s-1. In addition, one or two-electron oxidation of O-pentacene/nonacene generated the corresponding radical cations or dications, in which electronic properties were dependent on the number of O-containing six-membered rings and quinoidal subunits. The study provided insights into the relationships between molecule structures and optoelectronic properties for the unique class of O-embedded PAHs.
PMID: 30632366 [PubMed - as supplied by publisher]