Orientation Studied by Polarisation Angle Photocurrent Anisotropy

Molecular Orientation Studied by Polarisation Angle Photocurrent Anisotropy 

In the case that specifically adsorbed metalloporphyrins exhibit an average orientation at the adsorption plane, the excited state population will be determined by the relative orientation of the electromagnetic wave of the excitation beam with respect to the molecular transition dipole. As the photocurrent responses are associated with adsorbed porphyrins, changes in the angle of polarisation will affect the overall intensity of the photocurrent. In order to quantitatively analyse this correlation, the transition dipole moment M must be expressed in terms of the jc, y, z coordinates, corresponding to the referential of the interface. 

Galvani potential difference for a bulk concentration of ZnTPPC of 1.0 x 10 °mol dm is illustrated in (a). The photocurrent anisotropy at 0.26V as a function of the ZnTPPC concentration is shown in (b). Reprinted with permission form ref.[35]. Copyright (2003) American Chemical Society. 

The previous analysis has so far shown that photocurrent responses are directly linked to specifically adsorbed metalloporphyrin at the liquid/liquid boundary. The interfacial organisation of these species is affected by a series of parameters such as the bulk concentration and the Galvani potential difference. In this section, we shall concentrate on the dynamic and mechanistic aspects associated with the photocurrent signal. The information discussed in the previous sections concerning lifetimes of excited states and surface coverage will be relevant to the estimation of the heterogeneous electron-transfer rate constant from the photocurrent data. 

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