PREPARATION AND PHOTOCURRENT PROPERTIES OF TIN DIOXIDE ELECTRODE MODIFIED BY POLYIMIDE LANGMUIR-BLODGETT-FILMS POSSESSING TETRAPHENYLPORPHYRIN UNIT

Polyimide Langmuir-Blodgett (LB) film containing tetraphenylporphyrin (TPP) unit was newly prepared on the surface of tin dioxide electrode by “Precursor method” (Electrode I), and the generation of photocurrent wasmeasured by the wet system. The photocurrent spectrum obtained was very similar in shape to the absorption spectrum ofthe LB film. The quantum efficiency of the electrode modified by one layer of the polyimide LB film was 0.178, and thevalues decreased with increasing the number of layers. The long term stability of the photocurrent of Electrode I was compared with that of the electrode possessing the monomeric TPP LB film prepared from a 1:1 mixture of monoamino-TPP and stearic acid (Electrode II). These two electrodes were stable under the irradiation of monochromatic light of 430 nm, while in the case of the direct irradiation of the xenon lamp, Electrode I kept the same level of the initial photocurrent for a long time, but Electrode II decreased to 50%within one hour. The absorption spectra indicated that bothLB films did not come off from the surface of the electrodes during the photocurrent measurements. The decrease of thephotocurrent of Electrode II was explained by the hydrophobicity of the surface of the LB film possessing the long alkyl chain and by the diffusing effect of the reducing agent in the electrolyte solution. © 1990, The Society of Polymer Science, Japan. All rights reserved.