Synthesis and Characterization of Oxygen-Embedded Quinoidal Pentacene and Nonacene

Abstract

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 ∼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 significantly increased further, in particular, a noticeable lower-energy peak at ∼790 nm for O-doping nonacenes N1-OH/OMe. By the thin-film-based organic field-effect transistor measurements, the relatively 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 perfluorobutoxyl 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.

A Unified Mechanism on the Formation of Acenes, Helicenes, and Phenacenes in the Gas Phase

“…[10] This time scale is much shorter than the time scale for injection of PA Hs synthesized in carbon-rich outflows of AGBs tars of some 10 9 years. [10] Therefore,t he presence of PA H-like material in the interstellar medium suggests that ac ritical synthetic pathway to PA Hs at low temperatures is missing.T he mechanisms elucidated here might fill the gap and can provide aunique route to PA Hs at temperatures as low as 10 K. These mechanisms are of interest in organic chemistry and can be linked to material sciences as they provide insight into reactivity,bond-breaking processes,a nd synthesis of extended p-conjugated systems involving acyclic precursors (vinylacetylene) with extensive applications as building blocks for molecular wires, [16] carbon nanotubes [17] and graphene [18] along with molecular organic semiconductors for organic field effect transistors [19] and organic light emitting diodes. [20] Briefly,ahigh-temperature chemical reactor was utilized to investigate the reaction of distinct anthracenyl and phenanthrenyl radicals ([C 14 H 9 ]C)w ith vinylacetylene (C 4 H 4 ).…”

“…Therefore, the presence of PAH‐like material in the interstellar medium suggests that a critical synthetic pathway to PAHs at low temperatures is missing. The mechanisms elucidated here might fill the gap and can provide a unique route to PAHs at temperatures as low as 10 K. These mechanisms are of interest in organic chemistry and can be linked to material sciences as they provide insight into reactivity, bond‐breaking processes, and synthesis of extended π‐conjugated systems involving acyclic precursors (vinylacetylene) with extensive applications as building blocks for molecular wires, carbon nanotubes and graphene along with molecular organic semiconductors for organic field effect transistors and organic light emitting diodes …”

A remarkably strained cyclopyrenylene trimer that undergoes metal-free direct oxygen insertion into the biaryl C–C σ-bond

“…We revealed that this unusual reactivity originates from the intense intramolecular energy in the highly strained structure. Besides, recently, O-doping of polycyclic aromatic hydrocarbons (PAHs) is emerging as a powerful strategy to tailor the optoelectronic properties of π-conjugated molecular modules 42. This study presents a new concept for the preparation of potential sensing agents and O-doped PAHs.…”

Self-assembled graphene-based microfibers with eclectic optical properties

“…The aforementioned observations about the presence of the colorful species are most likely attributed to the O-doped PAHs with different sizes of π-conjugated systems formed as a result of NOG nanosheets decomposition. In fact, tailoring of the PAHs' electronic structure with the purpose of acquiring novel optical properties comprising color and PL by means of bottom-up synthesis of oxygen-embedded π-conjugated systems has been well documented [49][50][51] . In this respect, a study focused on the O-annulation of PAHs for the synthesis of different compounds with diverse band gaps, colors and PL emissions has great conformity with the observations regarding the NOG fibers 52 .…”