Abstract: The effects of the number and the location of hydroxyl substituents on electrochemistry, EPR and transient photovoltage properties of a series of hydroxyphenyl porphyrins were studied for the first time. The study results indicate that all oxidation-reduction reactions occur on the macroring of porphyrin. With the increase of the number of the periphery substituents of porphyrin, the conjugate system is getting to be easy for oxidation, difficult for reduction. An increase in structure symmetry would cause positive shift of half-wave potential values. Thereinto the electron-donation effect of the porphyrin compounds on their electrochemistry property played a main role. At the normal state, porphyrin molecules do not have EPR signal. However, light excitation may cause a transition of porphyrin molecules from singlet to triplet. At the same time, the change from diamagnetism to paramagnetism occurred to porphyrin molecules. In this case, the two un-paired electrons are nearby each other and cause a strong interaction, giving EPR signal with sharp peak at g=2.000. The g value increased with an increase in electron cloud density. Time-resolution photovoltage is generated from the free photoacoustic carrier. The decay of photovoltage is closely related to the molecular structure and the separation velocity of their charge, which decreased on the whole with an increase in the number of periphery hydroxyl substituents.

Key words: Hydroxyphenyl porphyrin, Electrochemistry property, EPR property, Time resolution Photovoltage property