Photoinduced electron transfer at liquid/liquid interfaces. Part V. Organisation of water-soluble chlorophyll at the water/1,2-dichloroethane interface

The molecular organisation and photoreactivity of water-soluble chlorophyll (CHL) are studied at the polarisable water/1,2-dichloroethane interface vi a photocurrent measurements. In the presence of ferrocene in the organic ph ase, photocurrent responses were observed as a result of the heterogeneous quenching of adsorbed CHL species. The magnitude of the photoresponses incr eases with increasing Galvani potential differences with respect to the org anic phase. The photocurrent dependence on the bulk concentration of CHL in dicated that the dye exhibits a strong affinity for the liquid/liquid junct ion. Furthermore, the behaviour of the photoresponses as a function of the Galvani potential difference suggests that partial protonation of the perip heral carboxyl groups takes place at the interface, decreasing the overall charge of the adsorbed species. The average molecular orientation of the ad sorbed CHL was estimated from photocurrent measurement employing linearly p olarised light under total internal reflection. It was observed that the pr eferential molecular orientation was fairly independent of the applied pote ntial and surface coverage. It is suggested that the interfacial stabilisat ion of CHL is determined by amphiphilic properties arising from the non-sym metric distribution of the peripheral carboxyl groups.