Delimited Polyacenes: Edge Topology as a Tool To Modulate Carbon Nanoribbon Structure, Conjugation, and Mobility

Carbon nanoribbons offer the potential of semiconducting materials that maintain the large charge-carrier mobilities of graphene. Here, starting with polyacene as a reference, we present a theoretical investigation as to how polycyclic aromatic hydrocarbons inserted into the polymer structure modulate the edge topology of the zigzag polyacene. The variations in edge topology, in turn, produce nanoribbon structures that have electronic properties that span insulators to narrow-gap semiconductors. Clear connections are made among foundational models in aromatic chemistry, namely, descriptions in terms of Clar formulas and bond-length alternation patterns, and the nanoribbon electronic, phonon, and charge-carrier mobility characteristics. These relationships, for systems that are synthetically feasible from bottom-up, solution-based approaches, offer a priori and rational design paradigms for the creation of new nanoribbon architectures

Unusual Electronic Structure of the Donor–Acceptor Cocrystal Formed by Dithieno[3,2‑<i>a</i>:2′,3′‑<i>c</i>]phenazine and 7,7,8,8-Tetracyanoquinodimethane

Mixed cocrystals derived from electron-rich donor (D) and electron-deficient acceptor (A) molecules showcase electronic, optical, and magnetic properties of interest for a wide range of applications. We explore the structural and electronic properties of a cocrystal synthesized from dithieno­[3,2-<i>a</i>:2′,3′-<i>c</i>]­phenazine (DTPhz) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), which has a mixed-stack packing arrangement of the (π-electronic) face-to-face stacks in a 2:1 D:A stoichiometry. Density functional theory investigations reveal that the primary electronic characteristics of the cocrystal are not determined by electronic interactions along the face-to-face stacks, but rather they are characterized by stronger electronic interactions orthogonal to these stacks that follow the edge-to-edge donor–donor or acceptor–acceptor contacts. These distinctive electronic characteristics portend semiconducting properties that are unusual for semiconducting mixed cocrystals and suggest further potential to design organic semiconductors with orthogonal transport characteristics for different charge carriers