No abstract

The study of thin film molecular architectures is an increasingly important endeavor with respect to the development and characterization of materials ranging from liquid crystalline displays to receptor-based biosensors. Here we describe an apparatus capable of simultaneously acquiring broadband spectroscopic and electrochemical information on molecularly thin films deposited on a transparent electrode surface through a multiple internal reflection geometry. To demonstrate the capabilities of this system, the spectroelectrochemical behavior of a single, neutral copper phthalocyanine bilayer was evaluated.

No abstract

We report the first application of a potential-modulated spectroelectrochemical ATR (PM-ATR) instrument utilizing multiple internal reflections at an optically transparent electrode to study the charge-transfer kinetics and electrochromic response of adsorbed films. A sinusoidally modulated potential waveform was applied to an indium-tin oxide (ITO) electrode while simultaneously monitoring the optical reflectivity of thin (2-6 equivalent monolayers) copolymer films of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxythiophene methanol) (PEDTM), previously characterized in our laboratory. At high modulation frequencies the measured response of the polymer film is selective toward the fastest electrochromic processes in the film, presumably those occurring within the first adsorbed monolayer. Quantitative determination of the electrochromic switching rate, derived from the frequency response of the attenuated reflectivity, shows a linear decrease in the rate, from 11 x 10(3) s(-1) to 3 x 10(3) s(-1), with increasing proportions of PEDTM in the copolymer, suggesting that interactions between the methanol substituent on EDTM and the ITO surface slow the switching process by limiting the rate of conformational change in the polymer film.

This work describes the electrochemical copolymerization and spectroelectrochemical characterization of 3,4-ethylenedioxythiophene (EDOT) with a commonly used EDOT derivative: 2,3-dihydrothieno[3,4-b]-1,4-dioxyn-2-yl methanol (EDTM), on indium-tin oxide (ITO) electrodes, as a function of the EDTM/EDOT comonomer feed ratio. The potential of initial polymerization and the degree of optical contrast between reduced and oxidized states increased steadily with increasing proportions of EDTM. Reactivity ratios were determined by spectroscopic characterization of the copolymer film and by monitoring the depletion of monomer from the starting solution by liquid chromatography, following the formation of relatively thick PEDOT/PEDTM films. Average reactivity ratios of 1.5 ( 0.2 and 0.4 ( 0.3 were obtained for EDOT and EDTM, respectively, demonstrating preferential deposition of EDOT on ITO electrode surfaces. Significant differences were noted at low and high degrees of conversion, indicating changes in copolymer composition with film thickness. These results have real significance for the characterization of electron-transfer rates for the first monolayer of PEDOT/ PEDTM on ITO, determined by a new mode of potential-modulated attenuated total reflectance spectroelectrochemistry. 1