A linear phenoxytetrathiafulvalene polymer is physically adsorbed onto a metallic substrate by spin coating to produce a polymer-modified electrode whose electrochemical and optical properties are distinctly different from those of the metallic substrate. A combination of electrochemical (cyclic voltammetry, coulometry, and chronoamperometry) and spectral (vis-near 1R) measurements were used to characterize these films. The films were found to be reproducible in behavior, to be stable over a wide potential range, and to exhibit unchanging response over many thousands of cycles. The electrochemical activity of the polymer films results from the transport of electrons and charge compensating counterions through the polymer matrices. By varying the concentration and the nature of the electrolyte and from ac impedance measurements, the kinetics of oxidation in these films is shown to be limited by ionic flow into the polymer phase. Spectroelectrochemical data provide the first evidence for electronic interactions between sites on a modified electrode surface. Moreover, the optical data obtained as a function of potential strongly suggest that the electronic transport in these polymer films is not related to mixed valence induced electrical conductivity. A less specific process involving neighboring molecular group collisions which leads to electron transfer is suggested. The electrochemical properties of these polymer-modified electrodes are not limited solely to the TTF systems discussed in detail here, but rather are shown to be generally representative of a broad class of π-donor polymers. © 1980, American Chemical Society. All rights reserved.