Synthesis, characterization and modeling of stable radical functionalized monothiophenes

Abstract

The synthesis, characterization and modeling of two oligothiophenes bearing stable radicals are reported. The radical precursors 2,4-dimethyl-6-(6-(thiophen-2-yl)pyridin-2-yl)-1,2,4,5-tetrazinan-3-one (3) and 2,4-dimethyl-6-(6-(thiophen-3-yl)pyridin-2-yl)-1,2,4,5-tetrazinan-3-one (4) were prepared in a good yield (80–90%) by condensation of the appropriate thiophene-pyridine carboxaldehyde and 2,4-dimethylcarbonohydrazide. The oxidation of 3 and 4 using 1,4-benzoquinone in methanol yields radicals 5 and 6 (6-(3-thienyl)-pyridine-2-(1,5-dimethyl-6-oxoverdazyl)), respectively. All these new compounds are stable in air and organic solvents. Radicals 5 and 6 were characterized by EPR and Infrared as evidence by the shift of the carbonyl stretching of the precursors from 1629 cm⁻¹–1660 cm⁻¹ for the corresponding radicals. Ab initio molecular orbital calculations and spin densities were used to ascertain electronic properties of 3–6.

GRAPHICAL ABSTRACT

KEYWORDS:

• Verdazyl radical
• thiophene
• pyridine
• carbonyl
• LUMO

Acknowledgements

We thank Laurentian University for supporting this work. We are grateful to Dr. H. Joly for EPR measurements.

Disclosure statement

No potential conflict of interest was reported by the author(s).