Electromodulated Spectroscopy of Molecules Immobilized on Electrode Surfaces
Adolfas K. Gaigalas, L. Li, T Ruzgas
The article describes electromodulated spectroscopy of molecules immobilized on electrodes. Electromodulated reflectance (EmR) probes changes in the absorption properties of the immobilized molecules while electromodulated fluorescence (EmF) probes the changes in the emission properties. EmR can be applied to the study of electron transfer (ET) reactions between redox active molecules and the electrode if the molecular absorption is different in reduced and oxidized states of the molecule. Stark shift of the absorption line and transition dipole reorientation can be studied with EmR for redox inactive molecules immobilized on electrodes. The magnitude of EmF signal of immobilized molecules depends on the third power of the separation of the molecules and the electrode. Large changes in the intensity of fluorescence result when the separation changes by fractions of nanometers. Thus EmF is a sensitive probe of desorption processes. EmF can be applied to the study of monolayer formation and potential induced structural changes at the electrode interface. Together EmR and EmF can be used to measure modification of the fluorescence quantum yield induced by interface electric field. The two techniques, separately and in combination, are powerful probes of electrode surface properties and dynamics.