Products and mechanism of acene dimerization. A computational study

Area of Science:

• Computational Chemistry
• Materials Science
• Organic Electronics

Background:

• Acene reactivity limits applications in molecular electronics, despite high charge mobility in materials like pentacene.
• Understanding acene thermal dimerization pathways is essential for developing stable organic electronic devices.

Purpose of the Study:

• To computationally investigate the reaction pathways and mechanisms of acene thermal dimerization.
• To determine how acene chain length influences dimerization versus polymerization.
• To assess the impact of phenyl substitution on acene reactivity.

Main Methods:

• Density Functional Theory (DFT) calculations using M06-2X/6-31G(d)+ZPVE.
• Analysis of reaction pathways, transition states, and activation barriers for acene dimerization.
• Thermodynamic analysis of dimerization products.

Main Results:

• Acene dimerization pathways favor central ring formation or polymerization, dependent on monomer length.
• For hexacene and longer, polymerization via double cycloaddition becomes the preferred pathway.
• A concerted asynchronous mechanism is observed for benzene and naphthalene, while a stepwise biradical mechanism dominates for anthracene, pentacene, and heptacene.
• Activation barriers for dimerization decrease significantly with increasing acene chain length.
• Phenyl substitution on the central ring does not fully prevent dimerization through other sites.

Conclusions:

• Acene reactivity can be tuned by chain length, favoring polymerization over dimerization for longer acenes.
• The mechanism of dimerization varies with acene structure, impacting reaction kinetics.
• Computational insights provide a foundation for designing more stable acene-based materials for organic electronics.