Regiochemistry in the electrochemical assisted grafting of glassy carbon. With focus on sterical hindrance of lateral chains in the electroreduction process of multi-functionalized bithiophene

The electrochemically assisted grafting process of glassy carbon (GC) surfaces is pursued by using the 7-[(5,50-diiodo-2,20-bithiophen-4-yl)sulfanyl]heptanenitrile (DIBHN). Which is an ad hoc synthesized bithiophene derivative: the DIBHN features two non-equivalent iodine substituents in the 5 (which is under the sterical hindrance of the sulfanylheptanenitrile group) and 50 positions. CV measurements show the occurrence of two reduction processes, the second, more cathodic one, induces the grafting. This result is in qualitative agreement with theoretical calculations (B3LYP/6-311G level of the theory) concerning the comparison of the optimized structures of the DIBHN neutral and radical anion species (first electroreduction process): the C–I bond length of the iodine in the 5 position varies from 2.098 (neutral) to 2.835 Å (radical anion), while the C–I bond length of the iodine in the 50 position remains virtually unchanged when comparing the geometries of the neutral and radical anion structures. Raman spectra are recorded for various polymer film thicknesses; the comparison with theoretical calculated Raman spectra further support the effective grafting of the glassy carbon surface.