Characterization and evaluation of role of porphyrin moiety in meso-tetrathienylporphyrin-polythiophene composite film

Porphyrin-polythiophene (pTh) composite films consisting of meso-tetrathienylporphyrin (TThP) and 2,2'-bithiophene (BiTh) were fabricated on transparent indium-tin-oxide (ITP) electrodes by the electrochemical polymerization of TThP and BiTh in solution. The incorporation of a porphyrin moiety to the pTh chain was confirmed by absorption and X-ray photoelectron spectroscopies. In the case of tetraphenylporphyrin (TPP), instead of TThP for electrochemical polymerization, no clear evidence of the incorporation of the porphyrin moiety into the pTh chain was obtained. In the presence of methylviologen and oxygen as electron acceptors, light irradiation on the TThP-pTh composite films generated stable cathodic photocurrents. A broad peak at approximately 420 nm corresponding to the Soret band of the porphyrin moiety was clearly observed in the photocurrent action spectrum of the TThP-pTh composite films. The photocurrent intensity of the TThP-pTh composite films was larger than that of the pTh film. The incorporation of TThP to the composite films was quite effective for generating larger photocurrents.