EPR investigations of β-deuteriated 5,5″-dimethyl-2,2′:5′,2″-terthiophenes

Abstract

The unambiguous assignment of the β-hyperfine coupling constants of the radical cations of 5,5″-dimethyl-2,2′ : 5′,2″-terthiophene (11) has been achieved by EPR spectroscopic investigations of the deuteriated compounds 12, 13 and 14. The syntheses of these substances were achieved by cross-coupling following the Negishi and Kumada reaction starting from deuteriated derivatives of chloromethylated thiophene derivatives. The generation of the radical cations was carried out by electrochemical oxidation at a constant potential in the EPR spectrometer. In the presence of acidic compounds a D–H exchange at the β-positions of oligothiophenes was observed. The experimentally determined spin density distribution was rationalized by means of semiempirical quantum mechanical calculations (RHF-INDO-SP). Theoretical and experimental assignments are in good agreement.