Abstract
Four possible atropisomers of meso-tetra (o-pivalamidophenyl) porphyrin, one of which is known as the picket fence porphyrin, have been prepared and their physicochemical properties examined. The visible absorption spectra of the isomers are all different, especially in DMF. The wavelength of the absorption maxima is most blue-shifted in the αααα-isomer. Phyllotype tendency, which is characterized by the relative intensity of the four bands in the visible region, was in the order αααα>ααββ≃αααβ>αβαβ. This is the same order as that of the blue shift. The order is also the same as that of the reduction potentials measured in DMF. The nuclear magnetic resonance (NMR) chemical shifts of methyl protons of the pivalamido groups are distinguishable among the four isomers even in a mixture of the isomers in chloroform or toluene. These results indicate that the conformation of the porphyrin (the distribution of the pivalamido groups between the two sides of the porphyrin plane) affects the physicochemical properties of the porphyrin. Interaction between adjacent pivalamido groups is considered to be responsible for this phenomenon.
