Sulfur-Doped Heptagon Embedded Polycyclic Aromatic Hydrocarbons as Non-Benzenoid Derivatives of Pentacene

Incorporating heteroatoms and non-benzenoid rings-such as pentagons or heptagons-into polycyclic aromatic frameworks represents a key approach for designing advanced optoelectronic materials. In this work, two novel pentacene derivatives, DSH-1 and DSH-2, were synthesized by embedding sulfur-doped heptagons into the conjugation backbone via efficient Ullmann coupling and acid-catalyzed Friedel-Crafts reactions as the key steps. Single-crystal analysis shows that DSH-1 adopts a curved bow-shaped structure, integrating an oxygen-doped pentagon and two sulfur-doped heptagons to form a unique 7-5-7 system. In contrast, DSH-2 features a 7-6-7 system and displays a Z-shaped conformation. Because of their difference in conformation, DSH-1 exhibits a significantly red-shifted absorption, superior thermal stability, and tighter intermolecular interactions, and shows p-type semiconducting property with charge mobility of 0.25 cm² V^-1 s^-1. Because of the nonplanar configuration of these two molecules, the sulfur atoms can act as anchoring groups in the single-molecule conductance characterization. In addition, DSH-1 can be oxidized to a radical cation DSH-1^•+ with red-shifted absorption around 650 nm and high stability, resulting from the enhanced aromaticity of the sulfur-doped heptagon rings after oxidation.