Photoinduced electron transfer at liquid vertical bar liquid interfaces. Part IV. Orientation and reactivity of zinc tetra(4-carboxyphenyl) porphyrinself-assembled at the water vertical bar 1,2-dichloroethane junction

Interfacial properties of zinc tetra(3-carboxyphenyl) porphyrin (ZnTPPC) sp ecifically adsorbed at the water/1,2-dichlorocthane (DCE) junction were elu cidated from the photoelectrochemical behavior under linearly polarized lig ht. The photocurrent responses originating from heterogeneous quenching by ferrocene did not show a significant dependence on the penetration depth of light into the aqueous phase. However, the photoresponses exhibited a rema rkable dependence on the light polarization for illumination in total inter nal reflection. These studies provide a rather unique insight into the corr elation between interfacial reactivity and molecular orientation. The avera ge tilting angle of the transition dipole moment appears to be directly rel ated to the surface coverage. Finally, photocurrent responses are strongly decreased with increasing pH of the water phase. This result suggests that the self-assembly propel-ties of ZnTPPC at the water/DCE interface are link ed to cooperative intermolecular hydrogen bonding involving partially proto nated carboxyphenyl groups. The implication of these findings concerning so lar-energy conversion as well as the molecular structure of liquid/liquid j unction are briefly discussed.