Definition
C22H14 is the molecular formula of pentacene, a polycyclic aromatic hydrocarbon (PAH) consisting of five linearly fused benzene rings. Its systematic IUPAC name is benzo[1,2‑b:3,4‑b′:5,6‑b′′:7,8‑b′′′]tetracene, and it is also known as 2,3‑dibenzanthracene or dibenzo[cd,lm]pyrene.
Overview
Pentacene is a highly conjugated organic compound that functions as a p‑type semiconductor. It is a solid at room temperature, sublimating rather than melting, and is insoluble in most common solvents. Because of its extended π‑electron system, pentacene exhibits strong absorption in the visible region, generating excitons upon illumination. These properties have made it a model material in research on organic thin‑film transistors (OTFTs) and other organic electronic devices.
Etymology / Origin
The name “pentacene” derives from the Greek prefix penta‑ meaning “five,” referring to the five fused benzene rings that constitute its backbone, and the suffix ‑acene, which is used for linearly fused aromatic hydrocarbons (e.g., naphthalene, anthracene, tetracene). The compound was first reported in the early 20th century during studies of PAHs formed in incomplete combustion processes.
Characteristics
| Property | Value / Description |
|---|---|
| Molecular formula | C₂₂H₁₄ |
| Molar mass | 278.35 g mol⁻¹ |
| Structure | Five linearly fused benzene rings forming a planar, fully aromatic system |
| Physical state | Dark violet solid; sublimes at 372–374 °C |
| Density (estimated) | ~1.15 g cm⁻³ |
| Solubility | Practically insoluble in water and most organic solvents; limited solubility in chlorinated aromatics |
| Electronic properties | Highest occupied molecular orbital (HOMO) ≈ ‑5.1 eV; lowest unoccupied molecular orbital (LUMO) ≈ ‑2.9 eV; band gap ≈ 2.2 eV |
| Optical absorption | Strong absorption peaks around 580–660 nm, giving a violet color |
| Stability | Susceptible to photo‑oxidation; degrades upon exposure to oxygen and light, forming quinone‑type oxidation products |
| Applications | Organic field‑effect transistors (OFETs), organic photovoltaic cells, research into charge transport in π‑conjugated systems |
Related Topics
- Polycyclic aromatic hydrocarbons (PAHs) – a class of organic compounds composed of multiple fused aromatic rings, many of which are environmental pollutants.
- Organic semiconductors – materials that combine the electronic properties of semiconductors with the processing advantages of organic chemistry.
- Thin‑film transistors (TFTs) – electronic devices that use a thin layer of semiconductor material; pentacene has been widely studied as the active layer in organic TFTs.
- Charge transport – the study of how electrons and holes move through conjugated systems; pentacene’s high charge‑carrier mobility (up to ~1 cm² V⁻¹ s⁻¹ in single crystals) makes it a benchmark system.
- Photostability of PAHs – research on the degradation pathways of pentacene under illumination, relevant for both material performance and environmental chemistry.
All factual statements are based on publicly available chemical databases and peer‑reviewed literature (e.g., PubChem, NIST Chemistry WebBook, and peer‑reviewed articles on pentacene’s semiconductor properties).