Role of Hydrophobic Interaction in Controlling the Orientation of Dicationic Porphyrins on Solid Surfaces

The adsorption orientational behavior of dicationic porphyrins on clay surfaces in various solvents was examined. Addition of aprotic solvents to the aqueous solution containing the clay-porphyrin complex induced a large which leads to the relaxation of molecular flattening. From spectral shift to shorter wavelength. The blue shift turned out to be due to the orientation angle change of porphyrin, dichroic measurements on a waveguide, the orientation of the porphyrin was directly observed and found to be parallel to the clay surface in water and to be at a tilt angle of 68 degrees with respect to the clay surface in DMF. A thermodynamic study of the porphyrin orientation on the clay surface was undertaken. This analysis showed that the parallel orientation of the porphyrin was stabilized mainly by the entropy term, and the tilted orientation was stabilized mainly by the enthalpy term. Furthermore, the effects of different organic solvents on porphyrin orientation on the clay surface were examined, and strong correlation between hydrogen bonding parameters and orientation change was found.