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Journal of the American Chemical Society, Vol.141, No.5, 2169-2176, 2019
Synthesis and Characterization of Oxygen-Embedded Quinoidal Pentacene and Nonacene
Extension of oxygen-embedded polycyclic aromatic hydrocarbons (PAHs), in particular with a defined topology, is synthetically 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 similar to 699 nm) and narrowed energy gaps (down to similar 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 (epsilon) of the lambda(max) significantly increased further, in particular, a noticeable lower-energy peak at similar to 790 nm for O-doping nonacenes N-1-OH/OMe. By the thinfilm-based organic field-effect transistor measurements, the relatively ordered O-doping pentacene P-1-OMe possessed a hole transporting efficiency (mu(h)) of 0.00406 cm(-2) V-1 s(-1) in in-air fabricated devices, while O-pentacene P-1-PFB with two perfluorobutoxyl substituents witnessed an improved mu(h) 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.