EPR and UV−Vis−NIR spectroscopic features of radical ions of amino substituted thienyl ketones

• Electrochemically generated charged species of amino-substituted thienyl ketones were studied by in situ EPR/UV−Vis−NIR spectroelectrochemistry. • Stability of radical anions and radical cations is caused by their different molecular geometries. • Radical cations undergo C–C coupling forming redox-active dimers. A series of amino-substituted mono- and bis-thienyl ketones were characterized by means of cyclic voltammetry, ultraviolet−visible−near infrared (UV−Vis−NIR) absorption spectroscopy, and in situ electron paramagnetic resonance (EPR)/UV−Vis−NIR spectroelectrochemistry. The molecular structures of bis-thienyl ketones contain morpholine ( 3a–c ) or N,N ´-disubstituted amino ( 3d–f ) groups. The electrochemical reduction of the ketones leads to the formation of stable radical anions, and their EPR and UV−Vis−NIR spectral features were analyzed in detail. In contrast, the radical cations are not stable and undergo follow-up chemical reactions with formation of redox-active dimers. The EPR data and DFT calculations provide information about the charge/spin localization in the electrochemically generated radical ions.