Various electrochemically active π-conjugated polymers were synthesized by organometallic polycondensations. p-Dopable polymers such as polypyrrole, polythiophene, and polyselenophene exhibited a linear correlation between the ionization potential of the corresponding monomeric compound and the oxidation potential of the π-conjugated polymer with a slope of about 1.5. On the other hand, n-dopable polymers containing imine nitrogen or quinone unit showed linear correlation with a slope of about 0.75 between the electron affinity of the corresponding monomeric compound and the reduction potential of the polymer. Cyclic voltammetric analysis in solutions indicated that the oxidation peak current (i pa) is proportional to a square root of the sweep rate ( v 1 / 2 ) in many cases. For poly(3-hexylthiophene-2,5-diyl), the diffusion coefficient (D) calculated with the Matsuda's equation was 10−7 cm2 s−1 at a molecular weight of about 3000, and it decreased steeply with increase in the molecular weight.