The ion transfer and adsorption behavior of the free base of water-soluble porphyrins were studied at the polarized water/1,2-dichloroethane interface by potential modulated fluorescence (PMF) spectroscopy. The PMF response indicated the presence of adsorption process for all systems depending on the Galvani potential difference. The adsorption from the organic side of the interface was found for cationic meso-tetrakis(N-methylpyridyl)porphyrin (H2TMPyP4+) at potentials more negative than its formal ion transfer potential. The emission spectrum for the interfacial species could be obtained successfully by analyzing the dependence of PMF intensity on the wavelength, and the emission maximum wavelength of the interfacial species was significantly different from the bulk species measured in the aqueous and organic phases. It suggests that the solvation structure of interfacial species is modified from both the aqueous and organic bulk species. The presence of adsorption process for anionic porphyrin systems, meso-tetrakis(4-sulfonatophenyl)porphyrin and protoporphyrin IX, was also found by analyzing the PMF responses. (c) 2005 Elsevier B.V. All rights reserved.