Stable Expanded Porphycene-Based Diradicaloid and Tetraradicaloid.

Area of Science:

• Organic Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Expanded porphycenes are macrocyclic compounds with unique electronic and photophysical properties.
• Controlling the electronic structure and stability of these systems is crucial for developing new functional materials.

Purpose of the Study:

• To synthesize novel bithiophene-bridged expanded porphycenes with aromatic (34π) and anti-aromatic (32π) conjugation.
• To investigate the electronic ground state, radical character, and stability of these synthesized compounds.

Main Methods:

• McMurry coupling strategy for the synthesis of expanded porphycenes.
• Magnetic measurements (e.g., SQUID magnetometry) to probe magnetic properties.
• Theoretical calculations (e.g., DFT) to determine electronic structure and energy gaps.

Main Results:

• Successful synthesis of a 34π aromatic (1) and a 32π anti-aromatic (2) expanded porphycene.
• Both compounds exhibit an open-shell singlet ground state with significant diradical character (y₀=0.63 for 1; y₀=0.68, y₁=0.18 for 2).
• Small singlet-triplet energy gaps (ΔE_S-T) were observed (-3.25 kcal/mol for 1, -0.92 kcal/mol for 2), indicating facile spin state interconversion.

Conclusions:

• The synthesized expanded porphycenes possess inherent radical character due to their electronic structure.
• Exceptional stability under ambient conditions was achieved through effective delocalization of unpaired electrons within the extended π-conjugation pathway.
• These findings open avenues for designing stable organic radical materials with tunable electronic properties.