SPECTROSCOPIC, PHOTOPHYSICAL, AND REDOX PROPERTIES OF SOME MESOSUBSTITUTED FREE-BASE PORPHYRINS

Spectroscopic and photophysical properties of unsubstituted free-base porphine and several symmetric meso-tetraalkyl- and meso-tetraarylporphyrins have been studied. Detailed analyses of absorption and fluorescence spectra, fluorescence lifetimes and quantum yields, and H-1 NMR spectra, as well as molar extinction coefficients and redox potentials, are reported. The experimental data are correlated with trends in the structural features of these molecules predicted by molecular mechanics calculations, including planarity of the macrocycles and the dihedral angles about the meso C-C bond. Conclusions concerning the role of excited-state lifetimes of some of the aryl-substituted porphyrins are presented. The significance of these results is discussed in terms of light-induced electron transfer in covalently linked porphyrin-containing assemblies.