The pi-conjugated polymers poly-1 and poly-2 composed of vinylogous tetrathiafulvalene (TTF) units were obtained by electrochemical polymerization of 2,5-di(benzylidene)-1,3,4,6-tetrathiapentalene (1) or of its corresponding dimer 1,2-bis(5-benzylidene[1,3]-dithiolo[4,5-d]1,3-dithiole-2-ylidene)-1,2-diphenylethane (2). The polymers were characterized by cyclic voltammetry (CV), in situ ESR spectroscopy and in situ conductivity measurements to gain insight into the charge-discharge behavior and the electronic properties as a function of applied potential. Our results suggest that both compounds behave as conducting polymers exhibiting multistep redox activity. In situ ESR studies show that charge-discharge phenomena differ in the nature of the charge storage configuration depending on whether they are investigated during a cathodic or anodic scan. Reduction of a polymer film generated at an applied potential of + 1.6 V vs SCE allows for the detection of three clearly discernible maxima of the spin density at 0.60, 0.95, and about 1.25 V vs Ag, while subsequent reoxidation gives rise to only one spin density maximum at around 0.65 V vs Ag. Coulometric studies suggest that the spin density maximum at around 0.60-0.65 V vs Ag is associated with one positive charge per tetrathiapentalene unit of poly-1 while each monomer bears up to two charges at a potential of 1.6 V vs Ag In situ and conventional four-probe measurements of the electrical conductivity gave values of around 5 x 10(-5) S cm(-1).