Modulation of Open-Shell Diradical Character of Imidazole Quinoidal Systems

Area of Science:

• Organic Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Open-shell diradical molecules are of interest for organic electronics and spintronics.
• Controlling diradical character and stability is crucial for practical applications.
• Positional isomerism offers a potential route to tune molecular properties.

Purpose of the Study:

• To synthesize and characterize imidazole-linked quinoidal constitutional isomers.
• To investigate the effect of positional isomerism on diradical character.
• To explore strategies for stabilizing open-shell diradical systems.

Main Methods:

• Synthesis of 2,2'- and 4,4'-linked imidazole-quinoidal isomers.
• Variable-temperature 1H NMR spectroscopy.
• Electron Paramagnetic Resonance (EPR) spectroscopy.
• Density Functional Theory (DFT) calculations.

Main Results:

• Identical molecular formulas yielded isomers with distinct diradical characters.
• The 4,4'-linked isomers exhibited significantly higher diradical character (y0 ≥ 0.5) compared to the 2,2'-linked isomer (y0 ≈ 0.2).
• Enhanced π-electron delocalization in the 4,4'-linked isomers was identified as the cause.
• All synthesized isomers demonstrated excellent stability in the solid state for over a year.

Conclusions:

• Positional isomerism is an effective strategy for modulating diradical character in imidazole-linked quinoidal systems.
• The 4,4'-linkage promotes pronounced open-shell diradical character due to increased π-delocalization.
• The developed isomers are stable, suggesting potential for future applications in materials science.