In this paper the infrared spectra of metastable state metalloporphyrin (where the metalloporphyrin is the meso-tetraphenylporphyrinatomanganese (Ⅲ) chloride [TPPMn(Ⅲ)Cl] was investigated by in-situ FT-IR spectroelectrochemistry in methylene chloride (CH~2Cl~2) and dimethylsulfoxide (DMSO). The results show that the oxidation state sensitive bands of TPPMn(Ⅲ)Cl are 1490cm^-^1, 1344cm^-^1, 1204cm^-^1, 1010cm^-^1, 806cm^-^1, and these bonds move to low frequency with the centre metal's oxidation state depression. When the TPPMn(Ⅲ)Cl gives one electron loss to form monocation radical of porphyrin, the spectrum displays a special change, the 1287cm^-^1 peak is the characteristic absorption peak of [TPPMn(Ⅲ)Cl]^+ monocation radical.

Key words: INFRARED SPECTROPHOTOMETRY, SPECTROGRAPHIC ANALYSIS, ELECTROCHEMICAL METHOD