The electroactivity of tetrathiafulvalene vs. polythiophene: synthesis and characterisation of a fused thieno-TTF polymer

The polymerisation of a fused 2,5-dibromothieno-TTF derivative has been achieved using Ni(COD)(2) as the catalyst. Whilst higher molecular weight fractions are sparingly soluble, lower weight samples are soluble in common organic solvents. Cyclic voltammetry shows that the polymer undergoes two reversible oxidation processes at +0.71 and +1.10 V (vs. Ag/AgCl), respectively. The optical and electrochemical band gaps have been deduced by electronic absorption spectroscopy and cyclic voltammetry and are in the range 1.75-1.89 eV. Independent conductivity measurements by impedance spectroscopy and four-probe methods give values of 5 x 10(-7) and 7 x 10(-6) S cm(-1) for the neutral polymer. The highest conductivity for the doped material as a thin film (0.1 S cm(-1)) was obtained from a drop cast solution of poly(11)/TCNQ (1 : 2 molar ratio). EPR and UV-vis spectroelectrochemical experiments reveal that both oxidation processes are centred on the TTF unit of the polymer. Chronocoulometric experiments show that almost two electrons per repeat unit are released upon oxidation at +1.3 V.