FLUORESCENCE LINE NARROWING SPECTROSCOPY OF ZN PORPHYRINS

Fluorescence line narrowing(FLN) spectroscopy was used to study the vibrational features of Zn porphyrins, including Zn octaethylporphine, Zn mesoporphyrin, Zn deuteroporphyrin and Zn coproporphyrin, and the interaction of these porphyrins with their solvent matrices. A number of ground-state vibrational levels were identified for each of the Zn porphyrins. Six of these levels persistent throughout almost all spectra were analyzed in terms of contributions of specific internal vibrational modes of the porphyrins. A number of other vibrational levels were identified as characteristic of the peripheral substituents of Zn porphyrin. Phonon wing contribution in the FLN spectra increased with increased polarity of the solvent matrix, and the Stokes shift calculated from the conventional spectra was correlated with the strength of phonon coupling. Specific vibrational modes were found to couple differently with the solvent and to have different phonon wings. The conventional and energy-selected spectra of Zn coproporphyrin in 5 M guanidine HCl suggest that guanidine ligates to the Zn atom.