Development of the Instrument for UV-visible Electroreflectance Measurement for Analysing Redox Behavior of Adsorbed Monolayrs on Electrode Surfaces

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The new instument for UV-visible electroreflectance (ER) measurement having the following characteristics was developed.1. The instrument can be applied to measurement systems where the absorption spectrum of the oxidized form is different from that of the reduced form or where the amount of adsorbed species changes depending on the electrode potential.2. The instument has high sensitivity (sensitivity of 0.002% at potential-modulation of 5mV) and high stability. In addition, all electrode materials which reflect light can be used for the instrument.3. The electrode reactions of multi-component systems which take place at similar potential range can be separately detected by changing the monitor wavelength and the frequency of potential modulation.4. By investigating the Stark effect, the orientation of adsorbed molecules on the electrode surfaces can be determined.5. Both the real component and the imaginary component of ER response are separately detected, so that the rate of electrode reactions up to around 10^5s^<-1> can be measured.6. The ER measurement in the wide wavelength region between 200 and 900 nm is possible by using a xenophoto lamp or adeuterium lamp as a light source.The following new experimental results were obtained by using the developed instrument.1. The electron transfer reaction rates of cytochrome c through COOH-terminated alkantiols with various chain lengths were measured. The linear relationship between the logarithm of the electron transfer reaction rate and the electron transfer distance was obtained in thick thiol layrs, while a deviation from the linear relation ship was observed in thinner thiol layrs.2. ER measurements of tetraruthenated cobalt meso-tetrakis (4-pyridyl) porphyrin enable us to elucidate that the redox reaction of the cobalt center of porphyrin occurs. Conventional voltammetric techniques could not measure the signal of the cobalt center selectively.