The photochemical and photoelectrochemical properties of two porphyrin derivatives with different numbers of carboxyl groups were investigated. The two porphyrin derivatives are 5-(4-carboxyphenyl)-10,15,20-tritolylporphyrin (H2TClPP) and 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (H(2)TC4PP). The interaction between the porphyrin. and TiO2 is determined by the UV-vis spectra. Differences in adsorption behavior of the two porphyrin derivatives on the TiO2 electrode surface were observed. The IR data suggest that both of the porphyrins adsorb by bridging or bidentate chelate coordination on the TiO2 surface. Comparing the luminescence spectra of the two porphyrins in solution and the solid state, no spectral difference was observed. However, we found that the variation in the number of carboxyl groups has an influence on the fluorescence spectra of the adsorbed TiO2 electrode. Furthermore, we measured and compared the incident photon-to-current conversion efficiency (IPCE) and the light-to-electrical conversion efficiency of the porphyrin-sensitized solar cell. These results revealed that the number of functional groups influenced the photoelectrochemical properties of the cell.