Stable Cross-Conjugated Tetrathiophene Diradical.

Area of Science:

• Organic Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Tetrathiophene derivatives are explored for their electronic properties.
• Understanding diradical species is crucial for developing new functional materials.

Purpose of the Study:

• To synthesize and characterize a tetracyano quinoidal tetrathiophene with a bi(thieno[3,4-c]pyrrole-4,6-dione) core.
• To investigate the impact of cross-conjugation on diradical character and stability.

Main Methods:

• Synthesis of the target tetracyano quinoidal tetrathiophene.
• Computational studies to determine diradical character (y0) and singlet-triplet gap (ΔE_ST).
• Analysis of singly occupied molecular orbitals (SOMOs) and their spatial distribution.

Main Results:

• The studied molecule exhibits a diradical character (y0) of 0.61.
• A small singlet-triplet gap of -2.76 kcal/mol was determined, indicating a stable diradical.
• Cross-conjugation confines the diradical character to the molecular center, leading to a half-life of 262 hours.
• Diradical stabilization was also observed in anionic species, including a radical trianion.

Conclusions:

• The tetracyano quinoidal tetrathiophene demonstrates significant thermodynamic diradical stabilization.
• Cross-conjugation is a key factor in controlling the electronic properties and stability of such molecules.
• The findings open avenues for designing novel organic materials with tunable diradical properties.