As part of an ongoing study of the chemistry and properties of <i>N</i>-methylporphyrins and their metal complexes, we have observed that the excitation and emission spectra of <i>N-</i>methyltetraphenylporphyrin and <i>N</i>-methyltetra(<i>p</i>-sulfophenyl)porphyrin and their zinc complexes closely resemble corresponding spectra of chlorophyll <i>a</i>. We have characterized fluorescence spectra for these species in a variety of solvents commonly used for quantitative determination of chlorophylls. Quantum yields for the <i>N</i>-methylporphyrins are lower by approximately a factor of 10 than yields for chlorophyll <i>a</i> in such solvents as acetone, ethanol, and mixed aqueous/organic solvent systems. The yields are quite sufficient, however, for these species to be used as fluorescence standards. Solution of <i>N</i>-methylporphyrins are stable and the compounds can be inexpensively synthesized in high purity. The tetra (<i>p</i>-sulfophenyl) species are soluble in aqueous and highly polar organic solvents, whereas the tetraphenyl species are soluble in nonpolar organic solvents.
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