Spectro- and thermoelectrochemistry of sexithiophenes in solution

In situ electron spin resonance (ESR) spectroelectrochemical and thermoelectrochemical studies of the non-substituted α- and the alkyl substituted (in α,ω-positions) sexithiophenes as single molecules in solution are presented. Thus any influence of interactions of the molecules in the solid state is avoided. In nitrobenzene solution the life time of the cation radicals is sufficiently high to detect and characterize them by in situ ESR spectroscopy. Furthermore, the α-sexithiophene (α-6T) was found to form insoluble films at the electrode surface by dimerization and polymerization while no film deposition at the electrode was detected for the end-capped α,ω-dihexylsexithiophene (DH-6T). In thermoelectrochemical experiments with continuous heating during anodic polarization, the polymer formation appears to be completely stopped. Obviously, the thermal stirring prevents the deposition of the generated polymer at the heated surface. The voltammetric waves corresponding to the radical cation or even the dication formation keep maintained in CV with permanent heating as well as with temperature-pulse voltammetry (TPV). With heating pulses being too short to initialize convection, the behavior was found different from that with permanent heating. Here, the polymerization at room temperature even with a somewhat increased rate causes a film formation at the electrode.