π-Extended and Curved Antiaromatic Polycyclic Hydrocarbons.

Area of Science:

• Organic Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Aromaticity and antiaromaticity are fundamental concepts in organic chemistry, influencing molecular stability and reactivity.
• Synthesizing large, stable antiaromatic polycyclic hydrocarbons (PHs) is challenging due to their inherent electronic instability.
• Previous research has focused on smaller antiaromatic systems, with limited exploration of larger, more complex structures.

Purpose of the Study:

• To develop a novel synthetic strategy for creating large, kinetically stable antiaromatic polycyclic hydrocarbons.
• To investigate the electronic and structural properties of newly synthesized antiaromatic compounds.
• To explore the potential applications of these novel materials in organic electronics.

Main Methods:

• Synthesis of cyclopenta[pqr]indeno[2,1,7-ijk]tetraphene (CIT), cyclopenta[pqr]indeno[7,1,2-cde]picene (CIP), and dibenzo[a,c]diindeno[7,1,2-fgh:7',1',2'-mno]phenanthro[9,10-k]tetraphene (DPT) based on indeno[1,2-b]fluorene.
• Characterization using UV-Vis spectroscopy, cyclic voltammetry, electron paramagnetic resonance (EPR) spectroelectrochemistry, and X-ray crystallography.
• Fabrication of microscale single-crystal fiber field-effect transistors.

Main Results:

• Successful synthesis of three novel antiaromatic PHs: CIT, CIP, and DPT.
• These compounds exhibit narrow energy gaps (down to 1.55 eV) and high kinetic stability under ambient conditions.
• CIP and CIT possess planar structures, while DPT displays a curved π-conjugated system.
• Reversible electron transfer processes were observed, and cation/anion radicals were characterized.
• Demonstrated potential for use in organic electronics through field-effect transistor fabrication.

Conclusions:

• The developed synthetic strategy provides a new route to pentagon-embedding and curved antiaromatic PHs.
• The synthesized antiaromatic compounds show promising electronic properties and stability for advanced material applications.
• This work expands the scope of known antiaromatic molecules and their potential functionalities.