SPECTROELECTROCHEMICAL MEASUREMENT OF CHARGE-TRANSPORT PROPERTIES OF ELECTROPOLYMERIZED TETRAKIS(HYDROXYPHENYL)PORPHYRINS

Hydroxyphenyl-substituted metalloporphyrins have been electropolymeriz ed as films onto ITO substrates. An ether bond between the phenyl ring s of two monomers links the porphyrin units, leaving the porphyrin mac rocycles undisturbed. During electrochemical oxidation of the films us ing a 0.0-0.9 V potential window, a single, semireversible reaction is observed, with n similar or equal to 0.5 electron per porphyrin molec ule. The spectroelectrochemical characteristics of these films can be adequately described by assuming that two neighboring porphyrin units are involved in the progressive oxidation process, in agreement with t he changes in the absorption spectrum of the film. To characterize cha rge carrier conduction, diffusion coefficients for chemically differen t films have been determined. From the optical changes upon oxidation of the film, the diffusion coefficients for hole transport were found to be (1-2) x 10(-10) cm(2) s(1). No correlation was found between the value of the diffusion coefficient and the number of cross links per porphyrin unit. The average distance between vicinal porphyrin macrocy cles, therefore, most likely determines charge carrier diffusion.