Synthesis, characterization and modeling of stable radical functionalized monothiophenes

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.