Dichroic measurements on dicationic and tetracationic porphyrins on clay surfaces with visible-light-attenuated total reflectance

Complexes formed with synthetic clay minerals and dicationic and tetracationic porphyrins were prepared. The Soret bands of the multicationic porphyrins shifted to longer wavelength upon the formation of a complex with clay. The clay sheets themselves and the porphyrin molecules on the clay surface were examined by use of atomic force microscopy (AFM) and polarized visible-light-attenuated total reflectance (ATR) spectroscopy (PV-ATR) with a wave-guide system. The flat adsorption of the clay sheets on the glass substrates was confirmed by AFM. A theoretical treatment of the analysis by ATR spectroscopy was derived. The orientations of the multicationic porphyrin molecules on the clay sheets in water turned out to be nearly parallel (< 5 degrees) to the clay surface, based on the PV-ATR analysis.