Unconventional, chemically stable, and soluble two-dimensional angular polycyclic aromatic hydrocarbons: from...

Area of Science:

• Materials Science
• Organic Electronics
• Semiconductor Chemistry

Background:

• Polycyclic aromatic hydrocarbons (PAHs), particularly linear acenes like tetracene and pentacene, are key organic semiconductors for devices such as organic field-effect transistors (OFETs) and organic photovoltaics (OPVs).
• Longer linear acenes offer potential for improved device performance but suffer from poor environmental stability, including oxidation, photodegradation, and reactivity with fullerenes via Diels-Alder reactions.
• There is a critical need for novel organic semiconductor materials that combine high performance with enhanced stability for practical applications.

Purpose of the Study:

• To highlight recent advances in the molecular design of two-dimensional (2-D) polycyclic aromatic hydrocarbons (PAHs).
• To demonstrate how these 2-D PAHs achieve improved environmental stability while maintaining or enhancing device performance compared to linear acenes.
• To explore the structure-property relationships governing the stability and charge-transport characteristics of these novel 2-D PAH materials.

Main Methods:

• Development of new synthetic techniques to create stable 2-D PAHs with extended conjugation.
• Characterization of material stability using measurements in chlorinated organic solvents and assessment of reactivity with fullerenes.
• Device fabrication and characterization of organic field-effect transistors (OFETs) to measure charge carrier mobility and Ion/Ioff ratios.
• Computational studies, including Density Functional Theory (DFT) and Hückel molecular orbital calculations, to understand electronic structures, stability (Clar's sextet rule), and reaction kinetics.

Main Results:

• Novel 2-D PAHs exhibit significantly enhanced stability, with bistetracene derivatives being approximately 200 times more stable than pentacene derivatives in organic solvents.
• These 2-D PAHs demonstrate high performance in OFETs, with hole mobilities up to 6.1 cm(2) V(-1) s(-1) and excellent Ion/Ioff ratios of 10(7).
• 2-D PAHs show reduced reactivity with fullerenes compared to 1-D acenes, attributed to their geometry and electronic structure, making them suitable for organic photovoltaics (OPVs).
• DFT calculations provide insights into the electronic properties, charge transport parameters, and Diels-Alder reaction mechanisms, correlating molecular structure with stability and reactivity.

Conclusions:

• Two-dimensional (2-D) PAHs represent a promising class of small-molecule organic semiconductors that effectively combine high charge-transport properties with superior environmental and chemical stability.
• The enhanced stability and performance of 2-D PAHs, particularly their reduced reactivity with fullerenes, make them highly suitable for next-generation organic electronic devices, including OFETs and OPVs.
• Molecular design strategies focusing on 2-D structures and appropriate substituents are crucial for developing advanced organic semiconductor materials for fundamental research and practical applications.